Ah, I'd forgotten about the Cayenne in all the hullaballoo surrounding the new Range Rover Sport.Thought you might have done, which is why Porsche has launched a brand new model - the Turbo S. Which is borderline unhinged. OK, it's been out a few months now, but that does nothing to lessen its impact. Especially in bright red, with a bright red leather interior.But Porsche already has a Cayenne Turbo.It does, and with 493bhp, it's a nose-on rival for the 503bhp Range Rover Sport supercharged (which you can read about here). But maybe the 10bhp shortfall, not to mention the recent introduction of the 518bhp Mercedes ML63 AMG, plus the imminent arrival of a new BMW X5, made Porsche realise it was no longer top dog. So it's added an S to the badge and a lot more cash to the bill.What? How does it justify that?By also adding more power. The Turbo S's uprated 4.8-litre twin turbo V8 now champs about with 542bhp at 6000rpm and 750Nm of torque from 2250-4500rpm. This results in a 280kph top whack and the ability to scorch to 100kph in 4.5secs. It feels considerably faster than that.Really?Yep. I drove the Mercedes A45 AMG the other day, which claims 0-100kph in 4.6secs. This thing utterly monsters it. To be fair, the surrealism of an SUV that is a capable of such feats of acceleration, combined with the height you're sitting at and the sheer momentum packaged up, means the Turbo S probably feels a bit faster than it actually is. All the same, I've not driven another SUV with the same headbanging mentality. Everywhere you go, you charge. You need to have it in Comfort suspension with the Sport light unlit to calm it down a touch. Do that and you'll open the Cayenne up to its duality.It's a good cruiser?It's an exceptional cruiser. It's got eight gears and the second of them is good for 120kph. The eighth pulls about 70kph per thousand revs, so motorways are tackled at well under 2000rpm, and as a result economy hovers around 8.1-8.8kpl (Porsche claims 8.7kpl and 270g/km). It's quiet and well insulated inside, but the softness of the primary ride is offset by wheel grumble from the massive alloys - 21-inches across. It doesn't feel at its most natural in Comfort mode.Sport mode is what's needed then?No, because I think it's too stiff and jouncy for our roads. It tries so hard to control the movements of its 2215kg mass that the vertical hopping can become unpleasant and actually rob you of some confidence in the car.Is there a 'Goldilocks' mode?Normal works just fine. Now you can press the sport button to sharpen up the throttle and gearchanges and really make the most of this car. The huge 295/35 tyres grip so hard and the speed the Turbo S can carry around corners before unleashing its turbo torrent down the straights is mind-boggling. There's real ability here, backed up by mighty, mighty ceramic brakes (once you get into the meat of the travel).Any downsides?Well, yeah, it weighs over two tons and it's an SUV. Surprising how easy it is to forget that when you're tramping on, because my word does the Cayenne manage its weight well. My only proper complaint is the steering which is too slow geared for the grip and immediacy with which the front wheels turn - in other words you have to use more lock at corners than you feel is right. The steering is also too light and lacking in any feel. It's something else that dents your confidence slightly.What's the cabin like?A bit overwrought on our test car (pictured above) - red leather is a bit Eighties Lambo for my tastes. But have it in a subtler shade and you'll appreciate the chunkily padded seats, the sheer rightness of the driving position and the fabulous quality and control layout. The design might not have the Range Rover Sport's panache, but I think it has the edge in other areas. But not seat count - the Cayenne is a strict five-seater, where the beefy Brit offers the option of seven.Speaking of which, is it a better car than the Range Rover Sport?Ah, here's where you've caught us out. We can't tell you at the moment, as I never got a chance to drive the Range Rover, and Sam Philip, who drove the Range Rover, never got his claws into the Cayenne. From chatting things through we reckon the Cayenne has the edge for speed and dynamics, but the Sport makes a better fist of comfort and habitability. It also sounds better than the Porsche, which is bassy and roars at you from a distance, but not as rude as you hope it might be. That said, neither sounds as good as the Merc ML63 AMG. That makes a proper racket.Anything else you want to get off your chest?Chiefly that the Turbo S, while being the ultimate Cayenne, probably isn't the best. In fact you could consider it an irrelevance now the real world speed of the Cayenne S diesel is here with the combined promise of 12kpl and 0-100kph in 5.7secs from its 4.2-litre, 377bhp V8 diesel. Which also has the small matter of 848Nm of torque. And if you want a hardcore Cayenne, there's the GTS (which we've driven) - naturally aspirated 4.8, 414bhp, 0-100kph in the same time as the diesel. But sharper to drive, much sharper to drive. However, as one tool to defeat them all, the Cayenne Turbo S is ridiculously capable. I have to say that even in I'm-a-n*b red with porn star interior, it's one of my guilty pleasures. I'd give it an 8/10 if it weren't so stratospherically priced. Let's call it a good 7.