I am looking to find out what CFM rating carb is best for doing the carb swap.

My previous experience with LA motors says 600-650 CFM should be plenty for a 5.2 or 5.9.

However on the crate 5.9 Magumns sold with the carb, they are using a 750-800 CFM range. These are not race motors, they are just carbed 5.9s running a stock cam and head. Why such a large CFM carb on these?
Do the Magnums just flow so much better that they can and will use the additional? I think they had around 80 or so more horsepower than their LA counterparts IIRC maybe that too has something to do with it.

I just don't want to buy more than I need, but don't want to short myself.

Looking to run a 5.2 with a whiplash cam, using the current 2200 stall, 518, and 4.30 gears.