The P-38 gets better as you go higher. At 20,000 feet and up, it seems to perform as good as (or better than) the Mustang. As you said, it is very stable but you must remember to use your rudders to help your rolls and turns. You must also be careful to watch your speed and remember to use your combat flaps to provide more lift for the wings.
The P-51B climbs a little faster than the P-51D, and turns a little bit better than the P-51D at all altitudes, high and low. But, the P-51B compresses easier than the P-51D, has a worse blind spot behind you, and has fewer machine guns .
For me, the P-51B and P-51D seem to stall worse than the P-38 at high altitude. When a Mustang stalls a wing, it is very difficult to recover.
I don't know much about the P-47, other than the P-47-D30 is the better one of the three P-47 choices.
Also, for the Corsairs at high altitude, I prefer the F4U birdcage rather than the F4U-1D. The F4U will hold more gas, so you can spend more time climbing up without worrying about running out of gas. The F4U birdcage Corsair is also a little faster at high altitude than the F4U-1D.