I'm not sure about the F4U-4, but flyiny the F4U-1 against Yaks and Lags is suicide. We ran several of these scenarios in squad training. The result is almost always the same, in pilots of equal or near equal skill, if you don't kill the ruskie quickly, he will destroy you. You must have an e ad and a little luck.
Now, in the soccer war, due to numbers, Arlo and I found ourselves constantly flying the F4U-D vs. The F4U-4 in actual sim combat in the CT was only slightly superior to the D. I was able to record plenty of kills in 1v1 situations against the overperked F4U-4.
I don't know why the F4U-4 is even perked. There are several non-perked rides with better or very similar performance characteristics. The guns package on the -4 is nothing special, the 6x .50 cals. Now if you had the perfomance of the -4 along with 4 hispanos, that would be worth some perk points.
But back to the original point, I don't think the -4 will perform well, at least 1v1, against the 9U or the Lag 7.