depends on its application, the .030 over 305 I had in my 86 Elky ran to 6000 RPMs, I ran a 570 Holley street avenger on it.
my current 454 in my 75 stepside has a 770 Holley, probably more than I need since this motor never goes past 5000 RPMs. could easily get by with 700 CFM. John