One other consideration is the AA% of the hops. The higher the AA%, the more lupulin and oils, the more aromatic quality you'll get from the hops, therefore lesser quantity can be added to acheive the same level of aroma as a lower AA% hop, however it's all subjective to your personal tastes, where some prefer grapefruit and others prefer piny or resiny...and any combination of aromatics.
I think it will be a matter of trial and error to get to your personal threshold. I like to go with 2 oz of "C" hops in a five gallon corny, as a general rule but it also depends on the beer style I trying to emulate.