Quick summary from the article
The inside
X5M has a well-built interior, better than Cayenne. Material and quality feels more solid and with higher quality. X5M also have more complete safety equipment. X5M also offer better interior space.
Driving comfort
Cars with all these power and so quick around the corners rarely offer good comfort. However X5M offer better comfort than Cayenne. Very pleasent seat comfort and back seat is also more comfortable than Cayenne. Unfortunaly the seven-seater option for normal X5 isnt available for the M version.
Engine and gearbox
As predicted fuel consumption are awful for these cars. They both use more fuel than the carmakers claim. Topspeed for Cayenne is 280km/h and BMW offer M drivers package for 2450 euro with raised topspeed limit to 275km/h.
Driving dynamics
You hardly feel this is 2500 kg car you take around the corner , particularly the BMW. X5M have a higher slalom speed than the Porsche but the Cayenne is slightly faster around the track thanks to more sensitive responding steering and the carbon ceramic brakes. However the X5M is more safe to drive around the track, even with DSC turned off the car is easier to control. Cayenne exaggerates its movements and reacts more violently.
Conclusion
The fact that X5M wins this comparison is surprising. It convinces with better space offer, more pleasent comfort and lower basic price. The strenghts for the Porsche is the V8 engine, steering and ceramic carbon brakes.
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There are totally 36 different categories (Categories as 'environment and price' are excluded). BMW score higher in 25 categories. Cayenne score higher in 8 categories. Two of the categories same points.