I reckon mine has done even more than yours, and it's still perfectly fine.
Hell I've done 8,000rpm full launches on Hoosier Drag radials - clutch didn't miss a beat and still hasn't.
+1 for coppermix, it really is the only choice for someone that wants the best performance, best clutch feel. They are MUCH lighter than any other twin I've used - ORC, OS etc.
And all Nissan boxes are a little "notchy" in GTR's I've found (GTR/RB25), not one car i've driven has been like silky.
The Getrag 6-speed though does have a different feel to it, you can notice it soon as you drive.