Not trying to start a catfight here, but...
The original P-51A was designed around an Allison engine developing 1150 hp, in a very rapid wartime design effort. The P-51B/D had a 1500 hp Merlin and the P-51H's engine could be boosted to 2200 hp with water injection. However, once the two-stage Merlin was introduced the aircraft was regarded as a high-altitude fighter - sea-level to low-level (5000 feet = Reno) speeds were not above 370 mph for any versions.
500 mph and 3800 hp is another kettle of fish.