I get boost creep up to 10-12.5psi off an 8lb spring on a tial 38mm wastegate... (Precision hp 5862 is the turbo I run now) the higher creeps happen in colder weather of course. On my old garrett t3/t04e 50 trim I was getting a steady 9.5 psi off an 8lb spring. I run nismo 555cc injectors with a stock fuel pressure regulator and I've been alright up to 17lbs so far with afr below 12. Do yourself a favor and spend your money on quality injectors and a decent tune. A turbocharger will only exacerbate any weakness in your engine and exploit any shortcut/penny pinching route you take.