Lt. Karl-Heinz Ossenkopf's comparison with Mustang:
In normal combat maneuvers they were both about equal, however D9 had a little advantage. In a dive, Mustang was slightly faster.
His summary against best allied planes:
"Overall, we pilots of JG 26 were very pleased with these new machines. Yes, we were doubtful at first, but we became more confident and felt we at least were equal or in some cases, even better allowing us to win the battle in a Fw 190 D9."
Source: "The Focke Wulf Fw 190 Dora", Jerry Crandall