True I overlooked that. Physics says that moving the pads out farther from the center of rotation will produce an enhanced braking effect. But one needs to consider radius not diameter in this situation. The change in radius is not a lot...
i think +1.1" in radius? thats a substantial amount, even on a street car. the reasons after market brakes perform better are thus:
1) larger rotors add more radius, thus make braking easier/enhancing the feeling of braking.
2)
many times (not always, as in the case of the Cobra/Mach upgrade) aftermarket calipers will have more pistons to increase stopping power. more pistons= a bigger area for fluid to press against, thus providing more stopping power. this is why '00 Cobra R 4 piston > Cobra/GT 2 Piston and Willwood/Brembo 6 piston > all
3) Many times, the rotors are higher quality as well. stronger metal will better resist warpage, and larger rotors will absorb more heat. also, slotted rotors will dissipate heat better, thus greatly reducing brake fade. brake fade is a drop in braking performance due to heatsoak basically. brakes need to be warmed up, but not too hot.
4) pad material affects braking tons also. it may be one of, if not the biggest factor. im no genius when it comes to pad material, but there are many out there. metallic, semi-metallic, organic, ceramic. ceramic is supposedly the best performing b/c it resists heat the best and clamps better i think. again, not too sure about pad material.