Awesome thread.
The standard steel brakes are 15" front and 14.5" rear. Added to this is the fact they are 4-piston and 2-piston respectively. The F10 M5 only has single piston rears while the E9x was single piston all round and a half inch smaller both front and rear. Very much looking forward to this brake setup for my track days, finally the Porsche guys won't be laughing at how I needed to mod the stock system just to run consecutive laps.