The performance relies greatly on altitude. At 15000ft the Bf 109 K even with only 1.8 ata outruns F4U-1 by some nearly ten miles per hour [1] [2]. Look at that chart closely and the F4U is about even with the 109 at its supercharger critical altitudes. That was speed,
climb. [3] [1] shows that Bf 109 K climbs slightly better, but significantly better at around 12000ft. The F4U-1 pilot should seek to fight somewhere near any of its supercharger critical altitudes, and not at its supercharger gear switch altitudes. As for turn rate, the F4U-1 looks better by wing loading, but I cannot find proof that it indeed turns better.
Note: I used the F4U-1 because I cannot find any report of a 2.0ata Bf 109 K, and if I do, I'll bring up the F4U-4 to compare to it.
[1]
Spitfire Mk XIV versus Me 109 G/K
[2]
http://www.wwiiaircraftperformance.org/f4u/50030-level-final.jpg
[3]
http://www.wwiiaircraftperformance.org/f4u/50030-climb-final.jpg