It took one hell of an engine upgrade, superchargers, massive 14 ft props, higher octane fuel and many other advancements to get that extra mph ahead of the competition. Here are some figures.
P-47n Thunderbolt 460 mph at 30,000 ft.
Mk XIX spitfire 460 mph at 33,000 ft.
F4U-5 Corsair 470 mph at 26.000 ft.
Grumman F8F Bearcat 470 mph at 29,000 ft.
Dornier Do335 Pheil (Arrow) 477 mph at 33,400 ft
But the fastest fighter was the P-51H 487 mph at 25,000 ft.
The Do335 Arrow the Grumman F8F Beatcat and the P-51H never saw combat in ww2.