Hi,
here is the picture of fitting wheels from X5
BMW styling 227 (X3 E70)
10 x 20 ET 40 tire 275/40/ - very close to the suspension
11 x 20 ET 35 tire 315/35/ - close to the suspension but in the same time outstanding from the fender - looks not good
Last picture: 8x18 (OEM) vs 11x20 (X5)