I'm running the
BMW Performance rotors on the front. The rotors are the same diameter as the stock rotors, but are just drilled & slotted.
Rotary forged wheels have less material around the perimeter of the wheel and so has room for larger brake discs.
If you are thinking about track time, the calipers are the real problem. The 135 calipers use plastic pistons. Search around the BMW forums and I think you'll find some posts about the calipers being destroyed by track usage.