A GTR with an exhaust, stock turbos, Power FC, cam gears and 14psi will usually make in the region of 250rwkw so considering your car has larger turbos and cams, your current power output is a little down on what it could be.
I think the deciding factors will be:
A) Your Tune
B) The type of N1 turbos you are actually running (R32/R33 or R34?)
C) How much boost you plan to run
Also, are you running a full aftermarket exhaust ie larger front pipes and dump pipes at the moment?