True but a 440 runs fine with manifolds but headers are better for power, bet it would run fine with a with a 2 bbl at a cost to power, put a 750/850 on a stock 440 picks up a decent amount of power. Bet if you put a 390 4 bbl on a 440 would work better than people would think, My cousin Late Model 372 pulls strong to near 7000 rpm with a 500 cfm 2 bbl, carbs are pretty flexible. People could use the formula but they would be short changing themselves in power especially in a performance situation but they would definitely not worry about over carbing :)
I think carbs should come with 3 cfm ratings the conservative 1.5 hg for stock and maybe add something like 1 hg for performance and 0.5 hg for race.