Well handlebar rise will affect the difference too, but with 9" of rise (including dust cap, stem rise, etc) frame B (20.8/74) will only move your hand position forward 1mm or so over frame A (20.6/75). With more rise the difference becomes even smaller.
There are other variables in there too - standover and BB height will change things but only by a tiny amount, it's probably not worth even considering...