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Please do NOT use the P-47 as a comparison unless you factor in a bunch of things. Like the P-47 was good NOT for 430mph at 20,000ft but more like 406mph (give or take) while using 2325hp and water injection. it could do 430mph higher up.
The Reppu, at least the A7M2, while it had 2200hp for take-off was down to 1800hp at 6000 meters (19,685ft) (no turbo) which gives the P-47 almost a 30% power advantage.
When figuring speed please use the power available at altitude.
But please note that the Reppu was actually an older airplane than the Bearcat by about 1 to 1 1/2 years and was designed to be a more all round fighter than the Bearcat.
The A7M1 was officially clocked at 357 mph at 20,310 ft with a Nakajima NK9K Homare 22 rated at 1,570 hp at 22,475 ft
Wingspan = 45'11⅜" area =332.173 sq ft: length =36'0⅞"
Loaded weight = 9,722 lb: Power Loading =4.9 lb/hp
Armament = 2 x 20mm Type 99 Mod 2 cannon, 2x 13.2mm Type 3 mg.
A7M2 (almost identical dimensions, same wing area, armament) with Mitsubishi MK9A 1,800 hp at 19,685 ft = 390 mph: weight loaded = 10,406 lb
so roughly the same performance as the F6F-5, albeit probably more manoeuverable - Japanese pilots commented favourably on the latter, comparing the A7M1 with the A6M when using manoeuvering flaps!
It's funny the F8F lacked the engine power since it was running the same engine as the Corsair, just a different dash number. If I recall correctly the F4U-4 used the R-2800-18W and the F8F-2 used the R-2800-30W.
I think the Corsair was better at groud attack, but the F8F was the better air superiority fighter. Many Corsair fans won't agree, and you may be one. Good thing they were on the same side, huh?