i had 400bhp/400lb/ft thru my gearbox and it never broke - was trying to break it for 5 years - the only issue with it was a 3rd gear synchro as could never change gear quick or gear down properly.

took the abuse perfectly fine - in fact i still have it in my mates garage

I would try and go for the Euan (rapidcossie) had as that is well cheap for the amount of power they can take.