Well, at 12,000ft the Spitfire Mk XIV shares second place for fastest piston engined aircraft with the P-51D, being edged only by the Bf109K-4. All the other speed demons, F4U-4, Fw190D-9, La-7, P-47M, P-47N, P-51B, Ta152H-1, Tempest V and Typhoon I are slightly slower to very much slower at that altitude.