I'm running a 10-1/2" clutch in a '70 Roadrunner convertible with street tires & 3.91's. I'm pretty darn hard on my clutch for a street car....make that very hard on the clutch.... and I think I'm around 3800# or so. My car spit out a Hays streets/strip clutch the first time I made a hard 1st-2nd shift with only about 30 miles on the clutch. I replaced it with a 10-1/2" Centerforce and it has held up well so far (without using slicks or the nitrous).

Clutches don't seem to be made as well as they used to be. I had good luck in the past with both Hays & Zoom, but at least for Hays, their quality has dropped way off.

11" clutches will hold better and I would have switched to an 11", but my motor is already balanced with my 10-1/2" flywheel (& not separately balanced)... changing the flywheel would force me to re-balance the engine.