Years ago when I had my BBSC I took it to the track for a few runs. I'd never been before so I'm sure I was pretty hard on it then.
During the engine rebuild process, I decided to go ahead and replace it. That was ~49k.
To test if yours is close to slipping........short shift to 4th gear. Go about 30 mph and then put the gas to the floor and run it up to 70 mph or so. Watch the tach. Once you detect a slip, your track days are done with that clutch, but you can baby it on the street for another year.
The life of the clutch as you can see depends alot on ones driving habits. I would presume alot of the higher milage clutches are highway crusiers with long commutes or easy drives behind them.