http://www.schmiedmann.com/X_series/...age2.htm#16564
http://www.alloywheelsdirect.net/bmw..._gt_f07_alloys
two sites that give great info.
Btw, if you put those X6 rims to the front, you may have problem turning as they are too wide. Also, those spacer you will need to put on will add extra weight/stress onto the suspension. I would consult a tire/wheel shop for their opinion.