Carburetor cfm for a mild 318 build

The problem with that so call carb formula is that it does somewhat accurately tell you how much air an engine displaces at a given rpm.
The only thing is the way carbs are rated doesn't correlate. A carbs rating has little to do with how much air will flow through it it's more about how restrictive it is. Eg. say 390 500 650 750 1000 carbs rated at 1.5 hg, but actually they all flow 500 cfm just a different vacuum amounts "restrictions". 390 will be more restrictive and the 1000 will be less. Problem is what level of restriction is suitable to your application, tuneablity, driveablity etc.. vs power. And don't really need a formula for that we have seen what works and it's usually a lot more than that formula. Will a 500 cfm work on your car yes will it give up some power yes, most would run a 650 some even a 750 is a 750 needed and will it make a lot of power over a 650 probably not. Question is there gonna be any power difference between what most would run a 650 and is there any throttle response difference compared to a 500, I'd say 650 will make more power and there would be little difference throttle response.