Joseph is referring to a diagram I plaguarized from Stoptech's site because it did such a good job explaining the idea - otherwise it is explained with a jumble of numbers.
Their version was this:
Joseph has a somewhat unique combination of the Stoptech front kit (larger rotor, caliper spaced out, but smaller pistons) and it was helpful to demonstrate where I thought adding 40mm rear calipers would end up. Happily, it seems to have hit a sweet spot.
My version of the diagram is here:
In this diagram, "Stoptech calipers" means only the swap of the OEM calipers for the 36/40mm Stoptech calipers. "Stoptech kit" denotes the 36/40mm piston calipers
and their larger rotor (i.e. the caliper is spaced out.) The kit is theoretically not as effective as the calipers alone because spacing the caliper out gives it more leverage and moves toward front bias again. The 38mm rear caliper conversion (with OEM fronts) gives the same balance as the caliper-only. The 40mm rear point is with the OEM front caliper. Joseph has the
kit on the front and I wanted to make sure adding 40mm calipers didn't move him too far to the right.
This graph wasn't entirely made up. I plugges all the numbers of piston sizes, rotor diameters, number of pistons, etc, into the formula for clamping force that Stoptech provides on their site. That let me compare the different setups. From nearly 100 customers of the 40mm calipers and a much smaller number of 38mm customers, I am very sure of the left side and center points as far as driver comfort during braking. From some very limited information from Gen 2 ABS cars that disabled the ABS, I projected the point on the right. (The ABS rear caliper is 43mm diameter and I believe if just over the very brave or hairy edge of best performance.)