Some time ago we had a post that looked at weber choke size (or EFI 8 barrel venturi size) and used the formulas from Weber that approximated where the peak power for the motor would be.
TWM/Weber manifold flow
I'm sure these values are approximate, but it appears that some users have found them fairly accurate given some recent results. Contrary to what I thought the webers or single stack EFI can be fairly restrictive to a motor once the size of the motor and target RPM range climbs.
I took the formula and ran it through various engine sizes to produce the graph shown below. One thing to remember is a 48mm IDA or IDF does not have a 48mm opening - the carb must have a choke installed and the largest these carbs fit is a 44mm. So, if you don't have 44mm chokes, and many do not from Pierce, Inglasie, Top End, then you might have an even smaller diameter breathing hole than you thought.
Once you get up to about 342/347/351 inches of motor it becomes clear that a 48mm carb body with 44mm choke will put your peak power at 6500 RPM or lower. While the webers feed smaller engines to 7000 RPM+, not so with larger engines. I've seen some 427s with 48 IDAs too, and it is clear their peak power is going to be fairly low in the RPM range unless the carbs are modified to handle much larger chokes (I think they can go to 52mm).
Sure, its all theory and approximated as well, but seems to hold up pretty decently under experimental testing.
R