Very interesting post, much appreciated. I also consider myself an experienced stick driver, yet my performance on my ST is still off even after 9 months. Every once in a while I seem to get the starting and shifting right and it shows the car CAN be driven smoothly. But any time I try it is far from perfect, definitely drivable but a picky person would find faults.
I have greatly considered removing the clutch assistant spring, but I am a coward. I do not want to chance severe clutch wear or failure over something silly.
You have me considering this now. If it changes the shifting for the better as well as you describe this will truly be an insanely valuable mod.