just wondering what steps should i take next for more power, kinda want to keep my current turbo if at all possible. i want 350 to the wheels.

my setup: blacktop s13, GTIR t28, 480cc injectors, maxima maf, front mount, stainless o2 and DP.

i put down 300hp,290tq at 15psi. i heard this setup is good to 18psi safely. how good is the stock head gasket? i was thinking cams and 18 psi should get me there, but what cams should i get, keep in mind i need mid range and TQ for drifting, not all out power. what about the top speed intake manifold? i wouldn't mind a s15 exhaust manifold either.