Hi Mate,
Ive got a KE30 coupe running a 13bt also.
I'm making well in excess of 300rwk but thats on 22psi.
I'm running a shortended R31 rear diff,31 spline axles and a LSD centre with tramp bars. Never had a problem.
Also running the AU hopper stopper kit up front with R31 rear discs. Pulls up fine from 250km/h.
Hope this helps.