6000rpm? Surely thats more to do with head/cam/turbo spec than anything else?
Or is 6000 the safe limit before the crank snaps clean in half?

Its like when people do 2litre ZVHs and claim they dont rev above 5500, but its cause they still using a pussy T3 so by time its hit 5500rpm the turbo (esp the exhaust side) is all out of flow...
They put a bigger job on it (.63 T34) and suddenly it revs through no bother.