To get 600 HP, I would think you are going to have to spin more RPM than just 5500 RPM. Could be wrong, just thinking off the top of my head. Specs on your turbo camshaft?
If your camshaft will only make power to 5500 RPM, it sounds like you would be building a high torque engine & not so much a high HP engine. Cyl head flow capabilities.
Use as big a turbine wheel you can get away with, about an "S" trim from Turbonetics would be a good size, "Q" for quicker spool but more back pressure.
70-72 MM compressor wheel.
.84-.96 A/R for the turbine housing, depending on your goals & how much turbo lag is acceptable for you. Split entry turbine housing.
Lots of variables when selecting a turbo, compression ratio, auto trans, manual,, you want peak boost @ what RPM,, daily driver, track car, street car, focused more for the street? etc etc.
