Even this is a BMW X5 forum and I am a BMW fan, I would still go with the Cayenne GTS. Sometimes we have to accept reality that X5 is not any superior to SUVs in the same league. E70 or W164, W164 all the way.

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2002 X5 3.0 Siena Red
Premium, Cold Weather, Rear Climate Packages, 19" Wheels
Aluminum Running Boards, Clear Tail Lights, Clear Side Markers
Titanium Kidney Grills, Titanium Trunk Lid, Xenon Headlights
4.6is X5 exhausts, 35% Tint, Aluminum Pedals
2005 530I Mystic Blue
Premium Package, Sport Package, Xenon Headlights
18" Sport Wheels, 35% Tint all around
Mods to come: M-Tech Front Bumper, M5 Side Skirts, M5 Rear Bumper
Quad Exhausts, Style 172 19" Wheels