I am in the same situation as you, I have a 4.8i with the 20" sport package on order. Even though the offsets are close, I would be worried that the older Style 74 wheel would not clear the larger brakes of the new X5 (E70). For what its worth, I spoke to someone at Tirerack about winter wheel options for the car, and they indicated the options are very limited because of brake clearance. This is not the case for the older X5 (E53).
2007 X5 4.8i (Performance Center Delivery, Feb 2007)
Monaco Blue/Tobacco/Bamboo, Sport w/ 20" wheels, Running Boards, Premium, Technology, Cold Weather, Heated Rear Seats, Premium Sound, Comfort Seats, Comfort Access, Sirius
2008 M5 SMG (Feb 2008)
Space Gray/Black, Comfort Access, Premium Sound, HUD, Heated Rear Seats, Heated Steering Wheel, Multi-Function Seats, Power rear sunshade, Ipod and USB Adapter, Sirius