Oliver,
Deja Vu, I thought I replied already cuz I looked up my test data but maybe Exploder blew up while responding.

I had Gtech tested a stock 250-Powerglide-3.08 using 4bbl carbs ranging from 390cfm to 625cfm. There was no clear trend with CFM, it mattered a lot more that the carb was "happy" - right jets, good shooters, launch technique - you could "stomp" on the 390cfm but not the bigger ones. But if launched correctly, the 390cfm cut a 2.574 60ft and the 600cfm Carterbrock was close behind at 2.580 sec. That is too close to call by far.

In 0-60mph te 600cfm Carterbrock actually won, 10.13 sec vs 2nd place 10.21 sec for the 450cfm Holley. Again very close.

At 1/8 mile et:
11.238 450cfm Holley R4548
11.266 600cfm Carterbrock 1406
11.284 390cfm Holley R6390
11.324 500cfm Autolite 4100 c3af-t
To show how it depends on carb, some "similar" carbs ran
11.406 600cfm Carterbrock 1405
11.538 450cfm Holley R3492 before tuning
12.130 500cfm Autolite c5af-f before tuning, what a dog
Most of the 1bbl Rochester B carbs ran from 11.50 to 12.50 so those last couple 4bbls were real dogs before tuning.

A lot of this was really testing the primaries. The secondaries on the 390 opened about 1/2 way, on the 450 a little bit, on the 500 a little bit, and on the 600s hardly at all tho the secondary transition circuits did help.

Bottom line, if U have a 4bbl in any of these size ranges, TRY IT and play around, if it runs good then just chill and shop around til U find a good deal on just the right CFM. It makes some diff but not that much.