What also really changes the motor is a short runner high volume intake manifold. I made peak power at 6200 redline (367hp) 15psi with this custom q45/sheet metal intake. I really should have revved it out more and I would have got to 400 at that same boost level.
Whole setup is for sale if anyone is interested, but I'm on the other side of the country from the OP so it's not much help to him.