Resurrecting this old thread to post some updated info.

So it's looking like the southbend (bought in '09) has begun showing signs of slipping, but only when the engine/trans is not fully warmed up and occurs in conditions during peak HP/Tq @8-9psi boost (3k-4k RPMs). It's intermittent so will keep a close eye on it.

Aside from a couple launches, it's been babied since installed and have experienced zero issues. No "clutch braking" on inclined stop lights, no burnouts, nothing like that - just simple/easy daily driving. It hasn't given up completely yet and until then, it's still been great clutch and vouch for Southbend's quality.

In short, looks like it lasted roughly 9 1/2 years (70k miles, best guess). I hope this helps someone in terms of lifespan.