i used to have an x5 4.8i, it was awesome. i was sad to sell it, but i like the qx enoguh to make it ok. i've never driven the cayenne.
i like the looks of the q70, in the 5.6 version, but it doesn't get good reviews at all. i think if i were going to spend that much money on a car that size i would get a bmw 550xi.