The AFDU ran tests using a Fw190A-3(BMW 801 at 2700rpm and 1.42ata) vs Spitfire Mk IX (Merlin 61 at 3000rpm and 1.00ata(15lbs boost)) with the following results...
Speed:
2000ft: Fw190A 7-8mph faster
5000ft: Same speed
8000ft: Spitfire 8mph faster
15000ft: Spitfire 5mph faster
18000ft: Fw190A 3mph faster
21000ft: Same speed
25000ft: Spitfire 5-7mph faster
Climb:
Little difference in climb up to 23000ft, when the Spitfire becomes superior; the performance gap widening rapidly.
Acceleration, zoom climb, dive:
The Fw190A pulls away.