T-C, aero-engine 'rating' figures are established by type-test, scientifically, so whether you "believe" as such, does not enter into it.
If you wish to read the linked data, (which is obviously factory/Air Min sourced) relevant specifics such as - fuel type - are listed.
As for the measured relationship between boost/hp/speed gains shown graphically, here is an example from
earlier in Tempest development: http://www.spitfireperformance.com/must ... t-fig2.jpg
- compare with the chart in the article linked earlier above of the later Mk 6 , at +17.25lbs..
The ability of the Sabre to run hard was a major feature, appreciated by its pilots, such as F/O Ron Dennis, who with a
wingman ran his Tempest WFO for ~50 miles in hot pursuit of an Me 262 jet, before shooting it down, & he reckoned..
"The engine loved tough handling, & never objected to maximum revs or boost for extended periods."
His compatriot, top RNZAF ace & 122 Wingco flying, Evan Mackie agreed, saying:
" The harder you flew them, the better they went... they could be thrown around the sky like a piece of paper. "
& he'd turned down the opportunity to introduce the Meteor jet into the 2nd TAF, prior to war's end,
preferring the Tempest, (after trying the jet).
He also preferred the Tempest to the Spit, even though he had 800+ hours on them.
While the Spitfire used an earlier mid '30s NACA wing profile, ( & incidentally the US Navy F4U/F6F/F8F types
all used the same NACA profile as the FW 190) the Tempest/Fury used a "...special high speed section
developed by Hawker's, the thickness chord ratio at the root being 14% & at the tip 10%.
The maximum thickness is at 37.5% of the chord. The aircraft is thus able to fly & dive at very high speeds
without any adverse effect on stabilty or control" - ( Hawker factory specs).
USN aircraft designed for carrier ops are built to be robust enough, although the early F8F had a silly wing-tip shedding
feature incorporated ( & deleted when it proved fatal in practice), so I don't know what you mean exactly by suggesting that
"British" ultimate G-load factors were somehow "light", ( Tempest rated 13.9G, - quite robust) , perhaps you meant
constructional techniques, which in the case of the Spitfire, did need work to make the Seafire a practicable carrier plane.
The original Spitfires, even in the improved Mk XIV variant, were limited to Vne/diving speed of 470 IAS, & also did not
accelerate in the dive as quickly as the 109/190, let alone the US fighters, or the Typhoon/Tempest/Fury.
The Mustang did have a low drag wing, with its maximum chord set back (similar to the Tempest) & this was a major
contribution to being significantly faster, both in cruise & maximum speed than the Spitfire, indeed the Spitfire
required the fitting of the big Griffon V12 to keep pace, but even then could not cruise as fast as either P-51, or Tempest.