^^ Not necessary.... I have STOCK dump pipes, then a veilside exhaust system.
Yes it will flow better but for the power levels here they are not a must.
To answer the question above I am running STOCK internal RB26 motor with a few add ons... Power FC, HKS cams, 550cc injectors, Blitz SBC spec R, M's pods and of course the N1 turbos. My 326kw run was just starting to knock at around 21-22psi. I use 18psi daily which is around 300-310kw