Blackkers, chuck it into 4th gear and boost up a hill. You will either notice it slip or it won't slip and that's how I would determine.
My pink excedy lasted a few power runs on the dyno before giving up on the way home on the highway. This was 250rwkw
I am currently running a KB clutch from KB clutches in Sydney. Great service and amazing price, just call him and send him a dyno sheet or some specs of the car and he will do the rest