4028S was rated at 500 cfm.
That is the reason everybody in the sixties was bolting on a 650 to 750 cfm Holley on their 327 engines.
Carter only sold 375 to 500 cfm carbs back then (late fifties to early sixties), so to get more cfm rating you had to use two carbs such as appeared on the 283 Corvette engine or the 425 horse 409. Multiple carbs results in multiple headaches come tuning time, which is why one big Holley superseded two smaller Carter AVS or AFB's.
It is true today which is why Holley makes a Dominator in up to 1450 cfm in one carb (though they still sell twin 750 Dominators for BBC Pro Stock motors to put on top of a Wilson fabricated manifold for your museum piece since the Manufacturers pressured the NHRA into requiring EFI on their cars for the past four years now).
Carburetors still out perform EFI and the switch over slowed the cars down for two years running. They finally got multiple injectors to match the performance of a carb but the computer doesn't like the transition from free wheeling the clutch to a hard launch so consistency off the line still suffers (in case you wonder what is wrong wuih the drivers and tuners because the independents with out big bucks can't find traction off the line.