Sizing carburetor

And that’s why it’s difficult for me to pick a carb as you’d think you want to pick a carb by the cfm but with Holley it’s 100 more than eldelbrock. I’ve been looking at those two carbs, the Holley 670 street advenger, and also the quick fuel slayer 750
There's no magic formula for picking a carb, if you want optimal you may have to try some know some peeps came borrow from? Or go by the experience of the last 75+ years of people hot rodding and racing.