10 psi on a stock motor is less cfm and slower impeller speed than 10 psi on a good hci motor. All centrifical compressors have a sweet spot that they are most efficient as pointed out above. I don't believe anyone can tell you which is better for you, including a Paxton rep, w/o more info. There is a reason they offer more than one size for early Fords. Call the tech line and give them ALL the details of your engine for proper sizing.