Isn't braking ability ultimately limited by tire grip though? If you have enough grab to lock up the tires, you have maxed out your braking ability and then tires become your limiting factor in stopping. Feel free to correct me if I am wrong, I am very interested in this.

I can get my wheels locked up with the EBC greenstuff pads and R1 rotors just fine. Granted I am on 35" soft compound MT/R Kevlars, which aren't exactly made for good pavement stopping power.