Pappy pretty much got it, however IMO she flies more like the 1A (which I consider the best pure dogfighter of the 1-series Hogs) than the 1D, without the extra gas in the wings.
The -4 essentially takes the two main shortcomings of the earlier marks: rate of climb and acceleration, and does away with them. While she still won't catch a Spixteen or La-7 in an extended straight climb, it's GREATLY improved nonetheless, and as with all the Corsairs the zoom is INSANE. With six tons of airplane behind it, she WILL run down those Ponies and La-7s who think they can lose her in the zoom. Additionally, she's in the upper echelons in acceleration at all altitudes, and is one of the fastest props throughout the altitude range, especially above 10,000ft. Even some of the top dragsters like the La-7 and Spixteen barely manage a second over her in acceleration.
As Pappy said, the engine adds additional 450hp over the 1-series, and the four-bladed prop is a major leap over the three-bladed one on the earlier marks. Of the five Corsairs we have, the -4 is by far the best in the vertical.
She also has all the other strengths of the Corsairs: Fast, superb high-speed, handling (ESPECIALLY aileron and rudder authority) excellent guns, der Uberflappen, reasonably tough airframe (though I still think our R2800 is made of glass).
The F4U-4 is either at the top, or at the very least within the top 5-10 or so, of virtually every performance category. There's few, if any, ships in the game that have so many tricks over so many opponents. Assuming equal pilots, the F4U-4 WILL beat any other opponent more often than not.
Really, her only glaring flaw is endurance. As Masher pointed out she does have a rather short range on internal fuel, but she can take a drop tank and full internal and even with the extra weight and drag is still more than a match for most opponents.
