I did some number crunching. The PDF file (bureau of aeronautics of the Navy) have the f4u-4 speed stats in knots.
I converted thee numbers for the test with the AC combat laden with 1 150 gallon drop tank. That makes it even more impressive. Yep..these numbers are for a combat ready, external fuel carrying, f4u-4.
at 20,500 ft-- 452 MPH
at sea level-- 374 MPH
at 15,000 ft-- 435 MPH
max climbrate @ sea level- 4770 fpm
time to climb to 20K-- 4.9 minutes
Sounds like our F4U-4 may not be right. Unless, we have a diff AC than the one described in those Dep of Navy charts.