I'll take your word for it. It's just that I saw somewhere that the F4U reached optimal engine performance at 20,000 feet, unlike the P47 or P51 who do it higher. But then, even a zero was able to shoot down a B-29 at high alt so it probably isn't that much of an issue. More of loitering time at high altitude and have enough performance to both shoot down heavy bomber and engage bomber escorts. So, my last question: Who will win above 30,000 feet?