Adding some clarity here for the folks who are looking to upgrade to 750i or Alpina brakes in the front:
If you have a 550i(USA) AND If you want to upgrade for cosmetics, you can purchase the 750i/760i/ALPINA B7/B6 Caliper Carrier part number: 34216786829 and use your existing caliper housing. You will need to purchase the Brake Rotors for a 750i: 34 11 6 785 675/34 11 6 785 676
If you have a 528i/535i/550i(USA) AND If you want to upgrade for better braking, you will need to purchase 750i/760i/ALPINA B7/B6 Caliper Carrier part number: 34216786829 AND 760i/Alpina B7/B6 Rotors: 34 11 6 789 543/34 11 6 789 544 and pads kit: 34 11 6 794 464
Both of the above mentioned setups use rotors that are 374x36. The difference is that the 760/Alpina rotors have larger surface area since the hat is smaller and the pads are bigger
Lastly, for even better performance with BMW parts, you can upgrade to e70 X5m Calipers/Carriers/Rotors/Pads.. they are bolt on.
All of the above mods have already been done by users on this forum so feel free for further inquiries
