The whp per lbs of boost is incramental. Say 4lbs gives you 35whp, 5lbs would give you 46whp, 6lbs - 57, 7lbs - 70, 8lbs - 93 9lbs - 110 10lbs - 125. Not factual numbers here, just ruff estaments. as long as you can properly cool the intake charge, and supply the right A/F ratio, ever lb will give you slightly more whp then the last lb increse.