As the Spitfire MkV entered operational service in 1941, a fair comparison would have to be with the Allison-engined P-51 and IMPO the Spitfire would be the superior fighter.

A comparison between the Spitfire MkIX and the Merlin-engined P-51s which didn't enter production until 1943 would be much tougher and the P-51D would IMPO be superior.

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"Stand by to pull me out of the seat if I get hit" - Guy Gibson