My experience is of the four speed classic clutch set up on a machine with the usual carb/exhaust upgrades.
The overall clutch assembly is rugged enough but I haven't been able to get away with stock springs. I got by with new stock springs for a few thousand miles after I put in good quality Surflex plates, but in the end, I had to substitute three heavy rate springs for three of the originals. The clutch never slips now but the hand lever action is quite heavy.