Mercedes SL63 vs BMW M6 vs Bentley GTC vs Jaguar XKR-S CAR Giant Test

Published: 19 September 2013

Big luxurious convertibles always attract a certain opprobrium, like opera singers performing pop songs, as though what they do is not sufficiently full of gravitas or integrity.

But these four big convertibles – SL63 AMG, XKR-S, M6 and GTC V8 – are not show ponies, dressaging along on shiny alloys, making show-off trumpety noises, bedecked with soft leather chaise lounges for the cosseted elite. They’re proper quick, and proper vicious. Yes, even that orange Bentley.

The reason I know this is I just about caught one of these cars with a desperate whirl of panicky arms at the peak of an off-camber crest, as it spat violently sideways at very high speed, alarming a good number of local woolly ruminants, but alarming me rather a lot more – given the choice I like my mince to made of lamb, not me and expensive metal.

Rather than these cars’ usual foraging grounds in the Cote D’Azur or somewhere equally resplendent with caviar-laden blinis and champagne-laden girls, we’ve been sent into the damp, heathery expanses of North Wales, on weaving roads barely wide enough, with an unpredictable surface that has more random wet patches than a puppy training school, and sprinkled with suicidal sheep, to see which can truly offer up the largest silver platter of tasty treats for the impossibly rich. Great.

First up is the Mercedes-Benz SL63 AMG, with its 5.5-litre twin-turbo V8 and 556bhp, thanks in this particular case to the £12,530 AMG ‘Performance Pack’ which imbues it with an extra 27bhp, a limited-slip diff-lock and a sprinkling of carbonfibre trinkets.

Ours also comes with the ever-handy ‘Airscarf’ heater system, the ‘Magic Sky Control’ sunroof (£2610) that’s either clear or like the inside of a Chinese takeaway fish tank and, amazingly, AMG’s potent ceramic brake system, which adds a startling £10,025 to the overall price of nearly £150,000. At least the sheep can breathe a bit easier.

Then there’s the BMW M6, which is a bastion of parsimony next to the Merc. A three grand Bang & Olufsen sound system, featuring a cool central pop-up speaker resembling an ice-cream wafer, is the only big-ticket item to add to its £99,020 OTR price.

The Bentley GTC V8, incongruously vast in comparison to even the four-seater BMW, looks like a Hermès jacuzzi in its orange and brown colour scheme. I can’t help thinking that the two-and-a-half tonne weight, four-wheel drive and four useable seats makes it the outsider of this group. At least the price-tag compares.

It might be based on an old car, but the new Jaguar XKR-S has had a major going over. Its 5.0-litre V8 gets an uprated supercharger, allowing it to pour out 542bhp, and for £103,000 you get an uprated braking system with aluminium calipers, bespoke adaptive dampers, a fast-acting active diff lock that shunts torque to where it can be transmitted best plus an active exhaust, with flaps springing open under full chat for maximum effect.

The engineering and construction applied to all is top drawer. The all-aluminium XKR-S, with new superlight aluminium suspension, weighs in at a relatively sprightly 1730kg, the SL (once a byword for bloated, gouty excess) is similarly aluminium outside and in, with carbonfibre used in the boot lid, and scales less than 1900kg, while the M6’s aluminium, steel and composite build (the wings are plastic) can’t quite keep mass under two tonnes. The aluminium and composite GTC is still heavier than Snowdon though.

But it’s their stupendous engines and the sometimes hilariously bonkers noises they make that entertains most. Flooring the SL’s throttle results in trademark AMG flak – not one continuous roar but an incessant trail of small, deep, barked explosions, except now there’s a comical falsetto wibbly-bobble on top from the turbos, and with each of the seven gears reached, a punch of extra fuel burnt for good measure. And it’s the extra gear that makes it so quick – it reaches the boil more smartly than the Jaguar.

While the old SL was quick but felt heavy, this one feels more contained, and you can really push it hard through corners, where it stays extremely composed thanks to the ‘Active Body Control’ damping, and all that torque can be smeared lovingly onto the road through the limited-slip diff lock. There’s just vast amounts of traction.

The brakes would stop an airliner. They might lack some feel when cold, but once white hot they can be mashed as late as you dare and the thing stands on its nose, with never a hint of fade.
After the frustrated sewing machines of many other R cars, and thanks to those active exhaust flaps, the XKR-S is a supercharged Jaguar you can hear. It takes a while to build, due to six gears and the time the supercharger needs to screw up, but eventually its V8 shrills out a flat, hard metallic scream, and crackles like a straight-through-exhaust racer on shifts and lifts.

When you’re driving the XKR-S you become a bit paranoid, aware that anyone following can track every throttle input, or output, as the exhausts translate every exploded droplet of fuel into noise, whether it be held bravely flat through a corner, or left to blow in the hot tubes as lack of confidence betrays you.

It smells too, a petrolhead’s Oxo advert, with the pungent whiff of burnt petrol from the exhaust washing over those in its wake. Testament to just how much explodes outside of the chambers was the film of thick black crud covering the rear valance after a long session.

As you accelerate, the Jag’s horribly light slow-speed steering becomes a help, making the car feel lithe, agile and alive. It means you get all sorts of chatty feedback from what’s occurring under the fronts sent back into the steering wheel, which is unique in this company, as is the ability to get it into a big powerslide, or a big mess, very quickly. Of the four it is the one that leaves most of the control in the hands of the driver, although its active diff certainly helped keep me sheep-free on that rise.

No such drama in the M6, I’m afraid. With a couple of turbos too and a 4.4-litre V8 (the same as the M5) it pretty much matches the SL for power with 552bhp, but it seems contained and conservative by comparison, doing its thing with a flattish, anonymous roar.

Obviously it is lightning fast and, with four people aboard, would leave the GTC for dead – and them fairly dishevelled at the end of it. But unlike the M5 it does it with hardly any drama, apart from the incessant twinkling of the traction control light as it tries to contain any lateral movement. Then, if you find the right switch and lose some of the electronic assistance, the leap from nannyish control to swingeing oversteer is alarming. But on the whole, everything is less theatrical, the steering requires more turn, and on the brakes you instinctively understand the need to stamp harder than in the SL or XKR-S because it is such a long, big car. The M6 has two programmable M buttons, into which you dial your own menu of damper, steering and throttle responses. But surely there’s an engineer in Munich who knows better than I what constitutes the optimum set-up? With my rough maths I worked out there are 27 different combinations. It’s almost easier to get the lottery numbers right.

I’d driven the SL first and left Ben P in the M6 for dead, and felt pretty handy as a result. Until I drove the BMW, and realised it is a much slower car due to its lesser brakes and inability to get traction out of slow corners as quickly. Damn.

The Bentley’s 500bhp twin-turbo 4.0-litre V8 is the quietest here, but it makes a wonderfully British noise: the steady, deep chug of industrial toil, vast steam pistons in a Lancashire mill, Merlin engines at half chat, the brass bands of mining villages trumpeting their anthems.

Building Jerusalem in Wales’s green and pleasant land, it’s a noise that is intoxicating in its understated way – less crass and showy than the others. Even on throttle lift-off from one of its eight, snappy gear ratios, it emanates the solitary, buttoned-up ‘bomp’ of a lone Bofor.

Because of its four-wheel-drive system and weight, you need to drive the GTC differently. There’s not much fun to be had with heroic late braking and hard-on-the-throttle exits. To brake, you must find a spot where the mass isn’t asking too much of the chassis and then it will dig in like a back-row forward at a ruck.

You can also use that momentum to effect through corners, by turning in before the apex, hammering the throttle open and letting the big beast drift through, like Benjafield – the original Bentley boy – in his pomp.

At the start of our trip, there was much pointing and tutting over the all the Volkswagen parts in the GTC, such as the sat-nav and low-slung indicator stalks. Shooting fish in a leather-lined barrel perhaps, but Bentley really knows how to make big, special cars for this top-end market and, as time wears on, you notice the leather laid perfectly down the inside of the door sills and window frames where others have grey plastic, the brushed aluminium ingot bonnet release, the thick leather sun-visors, the art deco clarity of the dials and the way every surface is perfectly finished. And then you start to think: if you had to drive one of these cars every day, the GTC might well be it.

That’s not something you would say about the Jag. Frankly, it’s a bit of a mess to look at, and the cabin is tired. Apparently ‘computational fluid dynamics’ informed the design to maximise airflow and downforce, but the big crease that curves around the nose makes the thing look like the cartoon character Droopy, while the side whiskers and rear spoiler appear to have been created in an Essex lock-up by a couple of keen but amateur young modders. Where’s the discreet cool the R badge used to bring?

Inside, the XKR-S is showing its age too: narrow, hard seats with uncomfortable side bolsters, clicky gearchange paddles from a Commodore 64 joystick, an infotainment screen with the clarity of an Ed Miliband policy, and some low-rent plastics too. At slow speeds the steering is light and rather vague, with a decent amount of turn needed to get a reaction.

The Jaguar XKR-S has four seats and cloth covering, but the hopeless rear bench proves only useful for carrying the amazingly large sandwiches Ben Pulman brought along for our adventure.
The SL feels as if it hails from a different era to the Jaguar. Beautifully soft leather seats look like they’re designed for a super yacht rather than sports car, while the AMG steering wheel, with brushed aluminium paddles and Alcantara inserts, is worth a loving fondle. Carbonfibre inserts and the new round air vents make the SL’s cabin more appealing than even the SLS, but although I like the organic running lights and sharky side strakes, does the SL look too similar to the SLK now?

Cruising out of our base in Comfort mode, the SL63 rides better even than the XKR-S, partly because of the 19in Continentals compared to the Jaguar’s 20in P Zeros. With the super-cool wind deflector (which opens like a fan) deployed, and both Airscarf and heating maxed, having the roof down is no problem, even in the grip of a Welsh summer.

There’s noticeably more shoulder room in the M6 than the Mercedes-Benz, while the cabin is standard 6-series fare except for the lovely spidery M Sport steering wheel and a plethora of M badges. We counted 32 in total. Hardly a Q-car. Also, the plastic area where the roof sits was already starting to mark. The others sit on more hardy chrome.

All four cars power their roofs shut in about 20 seconds, with the SL just the quickest in our race, and its cabin is probably the least turbulent too, due to its more compact dimensions. Only the Jag offers any noticeable shudder. The rest are stiffer than this ‘summer’ breeze belching out of the Irish Sea – and I’ve forgotten my coat.

Unsurprisingly the M6 and GTC, with their wide, open cockpits, give occupants the biggest buffeting, but luckily the San Tropezed Bentley seems to have a blow torch behind its disappointingly plasticky vents. The M6, in contrast, makes do with my daughter’s Barbie hairdryer.

Of all the cars, the M6 is the one for which I can’t fathom what the brief was. Unlike the Bentley there’s not much rear space, and its brittle ride scuppers pretensions of comfort. That would be fine, but this BMW then fails to get anywhere near the other two for thrills. It falls between more stools than Lindsay Lohan on a big night out.

Which leaves the other three. The Bentley started out as the proverbial orange elephant in the room, but in many ways it fulfils its role of carrying posh people superbly and in comfort best, while having a spot of the devil about it when you’ve dropped the kids off at school and picked up your squeeze for a day’s illicit entertainment.

But working on the theory there’s a Range Rover on the drive already, practicality and cost be damned. It’s between the SL63 and the XKR-S. The Jaguar grows on you as the appendages have grown on it, and it is an utter joy to drive very fast. If a criticism of the car is that it’s a little old-school, then it is also its biggest asset: hairy-chested, lamb-chopped, Brut-slathered, bottom-pinchingly brilliant.

The SL63 is more technological to drive than the XKR-S, and faster, but slightly less fun, although everything is relative. What a fabulous thing has been produced, from a very old car.
The new SL63 is more complete, though. Yes, it’s vastly more expensive, but it rides better, sounds great, has a wonderful cabin and is amazingly fast with it. Welsh B-road or Boulevard de la Croisette, sheep botherer or supermodel taxi – the SL63 AMG does it all.

Words: Steve Moody Photography: Jamie Lipman

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