We ALL been there. About a month ago I was trading out the contra spring, and noticed the back of the clutch has wear marks where it has been STOPPING the torque drive from fully opening. 3mm wasted! This is the delta that has been on the ZX for 4 years! I compared it to the OEM clutch, and found the oem is beveled to avoid this. I made a 3mm shim to fix it, and gained 2-3mph (right before melting the umpteenith piston). So even when you Think you got it nailed... something new humbles you.
For all you guys running after market clutches, I strongly suggest removing the contra spring, and checking for interference on the Torque drive pulley. There may be 2-3 mph in it for you as a gift from Z.