im not saying you are wrong, there is huge debate over the actual cfm of the 4966. some say that carter never even published the actual ratings. from what ive read they are a 625. im certianly not going to debate over it. we can both pull information supporting our claims. there was one for sale here a while back and the guy looked it up and found it to be a 625 cfm. the "gurus" on moparts say the 4736 is a 600 cfm. i also read where some say the 4966 is a 630, but who knows, i dont use either , i run holleys.
as to the original question, some carbs are just better than others, even being the same exact size and model.