Alright, so I'm looking at the OP, and it appears all the front kits use the same size rotors, and the only difference is some use a wider caliper/pad?
Drawing a rotor over the caliper and then a smaller circle through the center of the pistons gets me the same effective rotor diameter as subtracting half the pad height, within about 1mm. I also compared that method to what is in the brake math spreadsheet for stock brakes and came up with about the same numbers as Josh has.
So, anyhow, that gets me an effective radius of 141mm for the wilwood 6pots and 328mm rotors.
I'm also going to assume that the bore sizes are 1.625 and 1.125 since those are round numbers. Then I converted it to mm, and came up with what I'm going to call a "brake torque coefficient" which is piston area x effective radius (so mm^3) and then divided by 100000 to get a reasonable number.
So here is what that works out to for a number of brakes:
Stock: 3.51
FHI 4-pot: 3.10
STI brembo: 3.91
CTSV 4-pot: 3.71
Wilwood 6-pot: 3.695
Wilwood 4-pot: 3.77
So given the same pads and line pressure the kit will give about 5% more brake torque than stock, which is pretty much the same as what @
sickmint79 came up with, although I got about the same change from cts-v 4-pots.