VW shared the original development of the Touareg with Porsche, which had for some time been plotting to move into this sector. But this was only after Mercedes had earlier shown Porsche the door when it had asked to co-develop the ML series. So both the Touareg and Cayenne share crucial components throughout their make-up but with enough nuances to make them subtly different to drive.

The V8 engine in the Touareg (VW really needs to sack the guy in the naming department; Sharan anyone?) is the same unit found in the nose of the latest Audi A8 and a mighty fine engine it turns out to be, pumping out 305bhp at 6200rpm and 303lb ft of torque at 3000rpm. Discovering these figures after living with the car for a few days was a bit of a surprise, as the Touareg had felt much livelier at lower revs than I remember the Cayenne S ever being, yet on paper the Porsche delivers slightly more torque and at lower revs (310lb ft at 2500-5500rpm, to be exact) and 35bhp more power at similar revs.

The other surprise was how much sportier the V8 felt than the otherwise extraordinary V10 diesel. That mighty oil-burner might lay claim to some quite incredible figures (try 553lb ft for size, or 313bhp) but is handicapped by having twin turbos that first have to stoke the engine into life before the real action arrives, by which time the athletic V8 Touareg has upped and gone.

The diesel is still an amazing engine though; it's the nearest you'll ever get to the feeling of the good old 6.75-litre V8 Bentley Turbo motor, with a crazy flood of torque at very low revs. The redline is at about the same point too, just over 4000rpm, but the best bit has to be the absolute absence of diesel clatter, either from inside or outside. Instead, there's a subdued, slightly odd V8-like soundtrack that reaches an aural peak just before the limiter steps in.

For all its strengths, though, I came away thinking this engine isn't the answer. It may produce the power but it feels a bit lethargic; it lacks a sense of urgency, and only really impresses when pulverising a motorway incline, or perhaps while towing a heavy trailer.

But the biggest criticism has to be the diesel engine's weight. Step into the V8 petrol again and suddenly there's not only beautifully crisp acceleration on offer, but that tedious, nose-heavy handling of the V10 diesel has disappeared. Now the Touareg snuffles out apexes with an eagerness the Cayenne would be proud of. Even at higher speeds there's a really nice sense of balance from the chassis which encourages you to hustle more than you'd ever expect.

Look at the spec sheet and you'll see why this is - the diesel engine adds a further 207kg directly over the front axle compared with the V8 petrol version. That's more than a lot of engines weigh fully dressed, so it's no wonder the handling balance goes to pot.

So the sporty model in the Touareg range turns out to be the petrol version, saving you a handy ΂£8645 over the supposedly quicker V10 turbodiesel. There's not much point ordering the 'S' version of the V8, either, as that's more to do with cosmetic enhancements rather than any performance gains.

But that still means spending at least ΂£41,800 on a VW and that grates with me. Spec a Cayenne S to a similar level and you'll part with ΂£48,559. But the Porsche is way too ugly to have around in daylight so I couldn't do that either. It just goes to show how right BMW got it when the X5 4.4i Sport was launched just over three years ago.

If you want a sporting SUV, and don't want to spend Cayenne money, the BMW dealer is where you should be heading rather than to Volkswagen's showroom. Some things never change.