X5 3.0 and 4.4 come with the same brakes - 13.1 front and 12.8 rear. The 4.6is and 4.8is come with the same size rear brakes (12.8) but larger front brakes (14.0). You can run 17" 18" 19" on the 3.0i and 4.4i. The 3 recommended tire options are 235/65R17, 255/55R18, or 255/50R19 F & 285/45R19 R.
The 'is models came with 20" wheels and tires. I don't know if you can safely run 17"'s on them but I wouldn't bet on it. At least from what BMW CA states, you can run 18"'s.