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The 109F4 was the pinnacle of 109 developement. It retained all the positive maneuverability aspects of the E model, while performance in the area of climb and speed was substantially increased. The 109F was devastatingly effective against the now obsolescent Hurricane, the P-39, various P-40 series, the I-16, Lagg-3, Mig-3, Yak-1 and even the Spitfire V had a difficult time against F's flown agressively using altitude based team tactics. In a 1941 arena, the 109F would be at the top.
All the 109's after the F suffered increasingly from too much weight and speed for the original wing and airframe design to deal with really successfully. In fact, the 109F was supposed to be the last of the breed, being replaced by the Me309. Unfortunately for the Germans, in late 1940 Hitler, Goering and Milch scuttled the developement of the Me309 in the early stages on the assumption that the war was won and further aircraft designs would be unnessesary. If you take a look at the Me309 design, you may be surprised to see how much it resembles the P-51.
