I have a 2006 Cayenne S, which replaced a 2002 4.4 X5.
The X5 could couldn't hold a candle to the Cayenne. After driving a friend's Cayenne S, I sold my X5 in a matter of weeks and bought the Cayenne.
I drink the Porsche Kool-aid all the way.
Now, however, I' considering the X5 (5.0) once again because of the HP, great 0-60 time, and sticker which is 15-20K less than a similarly equipped CS. Where the Cayenne really separates itself is in its cornering ability. I'll be interested to see how the 5.o corners. If they've impoved that I may take the leap.