Everyone has a different opinion when it comes to after market performance and I definitely don't profess to be an expert. That said I would be very leary about putting cross drilled rotors on the X because it is such a heavy ride...I would be affraid of warping and cracking, UNLESS you get them "frozen" there is a place that sells cryogenically frozen rotors which claim to protect against cracking. I have ordered all my brake components from DAVID ZECKHAUSEN, "Zeckhausen Racing" he is at the track the time and knows which brake components would be best for your specific needs and application. And yes I own a 4.6 and yes I have bought brakes from him, use his expertise and call him you won't be disappointed.

Tirerack told me they do not recommend drilled rotors, but say slotted is alright for the x5 , I just did the Brembo slotted rotors and they work and look great.

cross drilled rotors will give better performance, but what about the pads? are they wearing faster than with regular rotors?

Yes the X5 is a 5,ooo lb vehicle but we do not drive them like race cars. I personally do not even drive mine as hard as I used to drive my M3 or 911. Cars on the track use drilled rotors so they can absolutely handle the demands of an X5. Ever see the brakes on a race car glowing red from the heat???