If your carb is dialed in right, it doesn't make much difference what the CFM rating is. That's at wide open, and you aren't cruising at WOT. For the around-town stop and go driving you do, a smaller carb might be more driveable just because you won't have to deliberately "feather"the throttle at every start to avoid dumping a bucketfull of expensive fun juice down the tubes. For highway use in the real world, I get much better economy with a well set up AFB than even a two barrel, Ford, Chev, Dodge, all have AFB's, all work better than the stock ones did.
i have a 318 pickup with an ancient SP-2P intake, and it does make a noticeable difference to mileage by keeping the velocity up, but the power just isn't there.