Ok, here's a topical addition, a link to a write-up of the Tempest Mk I prototype - by Bill Pearce:
https://oldmachinepress.com/2020/10/05/ ... i-fighter/
& from the document archives of member here 'snowygrouch', a chart showing the mid-war
expectations of speed/altitude of British fighter developments (early enough that the Tempest
is still referred to as 'Typhoon II').
https://www.calum-douglas.com/wp-conten ... 1610737973
The Tempest I variant did not enter service, although it was very fast for a 1943 fighter, being powered
by a higher altitude rated Sabre IV, due to emphasis being placed on the tactical role (the USAAF had
the high-altitude combat role vs the German fighters covered via its 8th & 15th strategic air forces),
for the forthcoming invasion of Hitler's 'Festung Europa'.
The wing leading-edge radiator arrangement of the Tempest I did offer a ~10mph speed advantage
over the 'chin' type set-up (as utilized by the Typhoon), when compared with the Tempest V using
the same Sabre IV, but a couple of salient points ensured it wasn't deemed worthwhile, in the event.
1stly, siting of the radiators precluded the available space/usage of the leading-edge for fuel tankage
as fitted to the Tempest V - & 2ndly, the compact armour set developed for the Typhoon to protect
the chin radiator/engine area during tactical A2G sorties - could not be used, either.