Al,
I can say without question that in all the races I managed to win, I've never slipped the clutch at peak torque -- always well below. My focus was (and still is, when helping the people I assist in vintage racing) keeping the clutch engaged as much as possible, and working with a balance between engagement characteristics of the clutch, gear ratio, and exhaust pipe. Even in the 100cc Open engines I ran in road racing, peak torque of that engine was above 11,000, yet the fastest way around the track was typically slipping between 9400 and 9700, depending on the track.
Also... all clutches "creep" to some degree... even at near peak RPM. Messing with *how* the clutch engages, and also tweaking the setup so the clutch will pull hard a good bit below peak torque helps to lessen that creep at higher rpm.
Slipping at peak torque is (in my experience) a good way to cook lining (if it's a lined friction surface) and just generally overwork/overheat the clutch.
PM