I feel that the P-63 should brought to Aces high. It's performance would allow it to fit in perfectly with the low-level, rat-race style of fighting so often found in the Main Arena.
The P-63 was faster than all other U.S. fighters below 15,000 feet. It's rate of climb was superior as well at all altitudes up to 30,000 feet. Roll rate, with a peak of 110 degrees a second, was better as well. Turn rate was second only to that of the FM-2.
The only real drawbacks would be its range, 37mm cannon with rainbow ballistics, and performance inferior to P-51 and P-47 at higher altitudes.
Regards, Shuckins/Leggern