The 6.0-litre twin-turbo W12 motor powering this Speed version isn’t that much changed, either. Yes, its power output has been tickled up by another 10bhp to 626bhp, but given that this engine developed 552bhp in basic form upon introduction over a decade ago, that’s not such a leap.
Then again, and for these purposes at least, there’s some benefit to its consistency, for its role here is the provide the benchmark for the other car now pulling into the car park opposite the Storey Arms on the A470, the start point for most hikers on their way up Pen y Fan.
That car is, of course, the Mercedes-Benz S-class coupé, perhaps better known as the replacement for the CL. In S63 AMG guise as tested here, its 5.5-litre twin-turbo V8 has a trifling 577bhp but, lacking the Bentley’s four-wheel drive hardware, it weighs a quarter of a tonne less despite being both longer and taller.
The upshot is a fractional power-to-weight advantage to Mercedes that would matter little were it not backed by a monstrous torque-to-weight advantage, too. The Speed is Bentley’s fastest road car yet and it looks likely to be blown to dust by a Mercedes based on a pre-existing saloon with a smaller engine and fewer cylinders.
The price differential between them makes painful reading, too, for Bentley fans. At £156,700, the Speed costs over £30,000 more than its rival, money that the Merc buyer could spend speccing his car to the nines or just buying a brand-new Lotus Elise for a bit of fun on the side.
Read the Bentley Continental GT Speed first drive
And I can think of no other two-door car, save a Rolls-Royce Wraith, capable of making the Bentley look so small. But it does: the Mercedes coupé might sit on a shorter wheelbase than an S-class saloon but it still logs in at well over five metres in length, longer even than four-door rivals such as the Porsche Panamera and Aston Martin Rapide S. Its lines flow beautifully, but next to it, the Bentley looks taut, compact and purposeful.
Technologically, it is to the Bentley as a super-computer is to an abacus. Were the roads not so winding, a passenger could have happily whiled away the entire journey from south to north trying to figure out the full range of its functionality and still found work to do at journey’s end.
This is a car that uses cameras as eyes to control the suspension, the cruise control and even the steering – on the motorway, it really will drive itself. Tick the right boxes on the options sheet and you can have a seat with a longer list of massages than a five-star Bangkok hotel and a Burmester music system with more controls than an Abbey Road mixing desk.
But we’re not here to fiddle with gadgets, however enticing they may be. We’re here to drive and I make no excuses for falling on the S-class keys first.
The route up past Builth Wells, Llandridnod Wells, Rhayader and towards Betws-y-Coed and Snowdownia is one of the best drives anywhere on the mainland, especially if you keep off the A470 and stick to the often more direct and always less travelled B-roads.
It was always going to be a challenge for such cars. Despite their sleek lines, these are not pure-bred sports cars nor even purpose-built GTs. Both are spun off saloon car architectures (let’s not forget the Bentley’s Volkswagen Phaeton ancestry) and even the lighter Mercedes weighs the wrong side of two tonnes.
But at times, 663lb ft of torque can make even such evident avoirdupois seem irrelevant. Mercedes’ home-grown seven-speed transmission is annoying because it is neither as smooth nor as intuitive as the ZF eight-speeder in the Bentley, but once you’ve learned to lock it in a ratio and let the torque do the work, this is a mightily fast car, and by any conventional standard you like.
The four-wheel-drive versions available in left-hand-drive markets will pop sub-4sec 0-62mph runs all day long. And that engine! I am by both instinct and disposition suspicious of downsized turbocharged engines but this one is magnificent.
Its performance is not characterised by the turbos at all, merely helped along. They blow relatively little boost, allow for a double-digit compression ratio and, as such, offer neither lag nor impedance to the engine’s voice.
Throttle response is electrifying, the noise the very blood and thunder you’d dream of in such a car, and the thrust… well, it is simply majestic.
Sad to say, the Bentley engine struggles by comparison. The issue is not its relative lack of torque or that its extra power is entirely stymied by its additional weight, because this is still a massively fast car. But it can’t do the subjective stuff anything like so well. Its voice is dull and its throttle response slack by comparison.There is no joy in this engine and, to be honest, it has been that way since it was born.
We’re deep into mid-Wales and I’m fiddling with the S63’s chassis set-up, trying to decide if its Pendolino-like ability to lean into corners is an asset or gimmick.
I decide that on give-and-take roads such as these, where it sometimes struggles to distinguish between curves and cambers, that it’s best left alone and settle for Sport mode instead.
I can remember being blown away by how well the S63 AMG saloon handled, but that was by the hardly high standards that you’d expect from a luxury limousine. The bar is far higher here and the coupé is clearing it, but by less than I’d thought.
There’s an artificiality to the steering that makes the car difficult to place on the road, and despite the arsenal of electronic suspension trickery at its disposal, it lacks the iron-fisted body control that I’d expected.
Then again, these are tough roads and if the Merc is finding them hard, how is the Bentley faring? Oddly, every time I look in the mirror, it is still there and showing no apparent signs of struggling to keep up.
The reason why soon becomes clear. In every dynamic area save perhaps braking, it is objectively inferior to the Mercedes. Subjectively, however, it is a rather different matter.
Out here where there is no such thing as a constant radius bend, where the only thing that changes more often than the weather is the camber and surface of the road, it’s not torque or power that’s the chief determinant of your point-to-point pace: it’s confidence.
Read the Mercedes-Benz S63 AMG coupé first drive
And this the Bentley supplies. Its old-style hydraulic steering has a feel that you’ll not find in the Mercedes and, despite their passivity and relative technological backwardness, its dampers retain better control of the Bentley’s body.
There’s less pitch and heave, and in the medium-speed turns that characterise this part of the world, I’d call it the more nimble of the two, were ‘nimble’ a word you could ever use to describe a 2.3-tonne four-wheel-drive Bentley with a 6.0-litre 12-cylinder twin-turbo motor. Then again, it is shorter in the wheelbase than the Benz, and substantially so, so perhaps we should not be so surprised.
How concerned should we be about such issues? These are cars more sporting than sports and there are many who’d argue that there are considerations that should take their place ahead of mid-corner adjustability in the priority queue for such devices.
Which is fair enough, but when I turn my attention to less exciting but perhaps more relevant considerations, I find them harder to separate.
I should prefer the Mercedes because, again, if you think about it at all sensibly, it’s just the better car. Its ride is more deft and its interior more spacious in front, back and boot. It’s undoubtedly quieter at a constant cruise and there’s so much to play with in here that years from now you’d likely still be finding new functions that you’d hitherto never known existed.
Nor can you quibble with the cabin design, where Mercedes has been able to tempt traditional materials into entirely harmonious living arrangements with a post-modern dash of thrilling complexity and sophistication.
The Bentley has little to offer in reply and its dashboard, with its simple analogue dials and a navigation screen not unlike that in a Volkswagen Golf, seems antediluvian by comparison.
And yet there’s a sense of occasion in here, a feeling of well being amid those exquisitely judged and matched hides and veneers that speak of another set of priorities, an innate class that not even the Mercedes can match. For the less gadget obsessed, it is a wonderful place in which to pass time time.
Despite an entire day on the road, by the time we reach the foothills of Snowdon, a clear victor has still to emerge. Despite all the common ground they share, these are profoundly different cars.
Bentley has excelled itself in imbuing the Speed with a timeless quality that the Mercedes cannot match, but if it is performance, ride, refinement or space that matters most to you, the Merc is just better, as well as £30,000 cheaper.
Even in this relatively price insensitive part of the market, that counts. In hackneyed terms, the head directs you straight to the Benz, while the heart implores you to go for the Bentley. I decide to sleep on it.
Soon after dawn the following day, we finish shooting and I’ve rarely seen this part of the world look more beautiful. But I am tired, there are many long hours of driving ahead and time is short. Bentley or Mercedes?
At last, the decision is clear. I walk straight to the Bentley, take one last, wistful look at that gorgeous interior and then, and only slightly guiltily, settle into the Mercedes and head for home.
Read Autocar's previous comparison - New Vauxhall Corsa versus Ford Fiesta and VW Polo
Bentley Continental GT Speed
Price £156,700; 0-62mph 4.2sec; Top speed 206mph; Economy 19.5mpg; CO2 338g/km; Kerb weight 2320kg; Engine W12, 5998cc, twin-turbo, petrol; Power 626bhp at 6000rpm; Torque 604lb ft at 1700rpm; Gearbox 8-speed automatic
Mercedes-Benz S63 AMG coupé
Price £125,595; 0-62mph 4.2sec; Top speed 186mph (with Driver's Pack); Economy 28.0mpg; CO2 237g/km; Kerb weight 2070kg; Engine V8, 5461cc, twin-turbo, petrol; Power 577bhp at 5500rpm; Torque 663lb ft at 2250rpm; Gearbox 7-speed automatic
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