The Cayenne S diesel is quite low tech compared to the M50d. It makes good numbers (281kW and 850Nm) but so it should given that it's 4.2-litres. If the Porsche engine was in the same state of tune as the M50d it would make 392kW and 1036Nm, so it's nothing special.
And X5 has a better chassis anyway... Game over.