Actually, nobody knows the answer to these questions. Fighter pilots of all nations overclaimed kills anywhere from 2x to 5x their actual kills over the course of the war, depending on tactical circumstances and the conventions of the air arm or unit, as verified postwar from the loss records of the other side. This was all known to each side's brass at the time, but big kill numbers and lots of aces are good for morale, so they quietly used much lower and more reliable estimates for their own planning.
The majority of aces, who claimed 5, 6, or 7 kills, actually never got 5.
The total numbers and the kill ratios claimed for aircraft like the Hellcat are

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Although overclaiming was universal, it occurred more at some times and places than at others, and therefore we cannot reliabily compare not only the absolute, but even the relative numbers of kills credited to different aircraft in different theatres.
Heavy bomber gunners often claimed around 10x the number of aircraft that the enemy actually lost, which is Glyn's point. No kill tallies for B-17s or B-24s, individually or collectively, can be taken seriously.
One could do systematic analysis to get the real data, making heavy use of the records of the side whose aircraft were shot down, except that (1) there would be major gaps in the data, (2) the question isn't of enough importance to interest any real historian, and (3) the pseudo historians who dominate the WWII-aviation-history genre are much too interested in perpetuating the old myths to be interested in the project.
August