It gets fuzzy. Enlisted responsibility is not strictly below officer responsibility, it's just different and somewhat overlapping once you get to higher NCO ranks. A high ranked NCO could be on par with a GS-12 in terms of responsibility scope, though perhaps not in pay. I'd agree that low GS grades (say 5-9) are probably akin to E1-E4, but starting at E5 or so (AF) you start gaining responsibilities (either personnel or materiel) that are more akin, not in kind but in scope, to lower ranked officers.