A little non-standard view on the differences in performance of the two planes. Technical and mechanical, but very convincing. I hope you'll enjoy it:
Just a sidenote (or maybe two). Games tend to mis-represent the performance of both planes, and WoWP is certainly guilty of that too, to some degree. In the current state of the game I feel like Mustangs are slightly underperforming on high altitude, where - according to this video, and according to historical data - they were really shining. Misconception number two is more of a general myth concerning the Mustang, namely that it was a very good 'dogfighter'. Not quite. The main assets of P-51 was the operational range and high-altitude performance; it was a typical BnZ plane, and it was very good at it. Many late war designs (like high-altitude variants of Spitfire) were significantly more maneuverable than Mustangs at comparable altitudes, including near the maximum of the their ceiling, but had drawbacks that excluded them from performing the task the Mustang was designed for. Which was escorting strategic bombers on high altitude, not going dogfighting (Mustang was an escort fighter through and through).