A few things.... Climb data published for the F8F-1 was for MIL power at full combat weight (max internal fuel, with ammo). Not Combat Power with ADI. So, those figure represent being down a lot of hp and heavier. Moreover, those Navy "handout sheets" were notoriously conservative. On their F6F-5 sheet, the Navy listed the max speed as 379.5 mph (330 knots). They refer to this as MIL power, but it actually corresponds to something closer to Normal power. There is lots of actual test data that shows 391 mph at MIL power and 408 using WEP for the -5 Hellcat.
I think it just bugs you that a carrier fighter had better climb performance than the P-51H. By the way, 90" of MAP was never authorized in post-war service use. Wear and tear on the engine was excessive. By the end of 1946, Mustangs, including H models, were being transferred to reserve units, being replaced by P-80s as fast as the jets became available.
As to the record set by Rear Bear... Lyle Shelton and his crew were well aware that Rare Bear's much reduced wing area would require substantially high takeoff speed with a corresponding longer takeoff run. The issue of greater torque meant that power would have to added carefully (meaning slowly). Shelton believed that Rare Bear's climb rate (well in excess of 7,000 fpm) would be enough to offset the time on ground due to the longer takeoff roll. Events showed he was right. But, only just barely. You realize that Rare bear holds the 3 kilometer speed record for prop driven engine aircraft, right? 528.33 mph average speed, hitting 541 mph on one downwind leg.
Ah no, Ww, you are incorrect - just go back & actually read those F8F 'standard characteristics'..
The 'combat' condition lists a rating of 2,500hp ( 'wet' =/ADI/WEP),
a weight of 10,337lbs & an initial climb rate of 4,665ft/min..
So ~2,000ft/min less than the stunt-cat made..
The maths don't lie.. it just had to be a cheater-stunt,
& one which, would likely - not meet FAI 'stocker' or flight condition requirements..
Also ( & AFAIR) Rear-Bare, sorry, Rare-Bear, was properly prepped for that record, including reverting to optimum lift wing configuration..
If you have any mil-spec documents that show ( as the ones I have posted)
a Navy F8F making ~6500ft/min & what power/load-out ratings it took, then kindly post them,
that of course would provide strong evidence in support of what is - so far - just
anecdotal information ( & your opinion too, natch..).