Porsche Cayenne vs BMW X5 (Part 1)

All-new Porsche Cayenne S Diesel packs V8 power, but can it outmuscle BMW's flagship straight-six-engined X5?

Porsche is famous for its low-slung-sports cars, but its biggest-selling model in the UK is the Cayenne. The SUV is now into its second generation, and its once controversial looks have matured into an acceptable upmarket shape, while a classy cabin and superb handling have made it our class favorite.

But if there's one chink in its armor, it's the fact that the V6 diesel model lacks the warp-speed performance people expect from a Porsche. This has now been address by the new twin-turbo 4.2-liter V8 S Diesel, which has 850Nm of torque – that’s 150Nm more than the petrol Cayenne Turbo.

However, this isn't the only high-performance diesel SUV on the market. The X5 M50d Sports wears BMW's hallowed M badge and produces a near-identical 375bhp from its three-stage turbo 3.0-liter straight-six engine. And with an all-new X5 just around the corner, this blisteringly quick range-topper is out to prove that there's still life in the old dog yet. So which of our rapid, high-riding contenders makes more sense?

Porsche Cayenne S Diesel

V8 newcomer gives performer diesel SUV a shot in the arm

Thanks to their menacing size, brash styling and thirst for fuel, performance SUVs aren't universally loved

Thanks to their menacing size, brash styling and thirst for fuel, performance SUVs aren't universally loved.

So for most owners it's probably a good thing that the new Cayenne S Diesel doesn't shout about its performance quite as much as more extrovert petrol models such as the Turbo and Turbo S. The white paint, optional 21-inch wheels and black roof rails provide our test model with some menace, and the Cayenne's once derided shape has evolved into a smart. Well-proportioned design that's more modern than the dated X5.

Inside, you'll find the same first-class driver-focused layout as in other Porsche. With controls that wrap around you, the new model almost has a sports car feel and the quality of materials and switchgear is superb, plus the traditional five-pod Porsche instrument panel adds to the character.

Plastics are smarter than in the BMW, while our car's full leather interior and adaptive sports seats add to the cosy feel. There's a huge range of adjustment and the supportive seats give an ideal driving position.

Inside, Cayenne feels like a sports car with classy, driver-focused design. Quality is superb

Yet despite the sports car ambience, the Cayenne's size ensures you get a lofty view of the road and all-round visibility is excellent.

There's lots of cabin stowage and the rear seats slide and fold 60:40. Legroom is a match for that of the X5, but while the outer seats are sculpted and comfortable, the middle one is narrow and flat, so the BMW's single bench is better if you regularly carry three people.

Still, the Porsche has an extra 50 liters of luggage space, offering 67-liters with the rear seats in place. Obviously this is important, yet these SUVs trade as much on handling and performance as practicality.

The Cayenne doesn't disappoint on that score, either. As soon as you turn the key, the V8 idles with a smooth, yet purposeful grumble, while the optional sports tailpipes produce a surprisingly petro-like soundtrack. The 4.2-liter V8 is borrowed from Audi, but Porsche has fitted unique internals too deliver 41bhp and 50Nm more than this engine offers in the Q7. Coupled with a sporty throttle response, the quick-revving 377bhp twin-turbo provides instant acceleration, while the mighty 850Nm of torque gives a seemingly never-ending wave of thrust.

Performance from V8 diesel engine is breathtaking, yet Porsche is impeccably refined, too

At the test track, the Cayenne covered 0-60mph in just 5.3 seconds and was quicker to respond than the X5 in all but seventh gear. On the road it's almost unnervingly fast for a vehicle of this size and weight, although it has the dynamic ability to cope with this.

Reactions are sharper than the BMW's, and the steering is fast and precise with more natural weighting. Body movement is well controlled and, even though the X5 is only 30kg heavier, the Cayenne feels more agile.

There’s so much grip on offer that you'd do well to get close to the limit within the confines of the road, but at the test track you can feel the chassis hunkering down as the optional torque vectoring helps keep the Cayenne on its line. The Porsche is also more relaxing – it follows cambers in the road less than the X5, and with the $3,568 air-suspension fitted, the ride is cushioned and comfortable. However, the weight and size of the optional 21-inch wheels mean the Cayenne crashes into potholes, taking the edge off the otherwise excellent refinement. If you want to avoid this trait, stick with the standard 18-inch alloys.

Quad exhausts deliver soundtrack like a petro car’s; boot has 50 liters more space then X5

The eight-speed Tiptronic auto doesn't have the razor-sharp shifts of Porsche's dual-clutch PDK, but it's smooth and, matched to stop-start and coasting functions, helps economy. The car returned 29.3mpg on test, although it emits more CO₂ than the BMW, at 218g/km.

And while the Porsche is nearly $3000 cheaper than the M50d, you have to be careful not to get carried away with the options list-out test car nudged past the $112,500 mark with extras fitted. Nevertheless, the new Cayenne S Diesel's mix of performance, comfort and luxury is hard to ignore.