The rear M wheels won't fit the rear hubs on a standard X5 without boring the centers of the wheels to 74mm from 72.5 or running a spacer/adapter to convert from 74 down to 72.5 on your X5 (which is nice since it adds a 15mm spacer - here is one at ecs
http://www.ecstuning.com/Search/ES18...746/ES1899557/)