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Well, let's see. The P-51B only just made into service. The Spitfire XIV did not - but it was in production. The IX and VIII were in service. The Bf109G was in service. The Fw190A/F was in service, but I think the Fw190D missed.
The F4U and F6F were both in service.
The P-38J debuted in 1943. The Lavochkin La-5 was in service in 1943 too.
So, I 'm going to have to say the P-38J was the best fighter in service in 1943.
Corsair was able to carry just under 540 gals of fuel, total. La-5 under 130, Fw-190 under 200 gals, total?
R-2800 was perhaps 15% bigger than ASh-82 BMW-801, not great deal.
Corsair has the edge for being a de-bugged machine vs. P-51B, also having greater firepower. P-51 was faster, it had smaller logistical footprint (fuel needed to conduct the same missions).
if 175 gal were on drop tank because compare the others fighters (la-5 and 190) w/o drop tank. was this available in '43?
and the 124 gals on wing have SS tank?
and even with 361 gals this is around 3 times la-5 fuel and 2.5 times 190 fuel i've doubt that F4U can get 3.3 times radius