Rab, there must have been some sort of lead turn being employed here. It may not have been obvious to you, maybe cause of lag, or they used vert seperation rather than horizontal to pull it off - or a combo of both.
I can assure you the P51 cant out turn a spit at slow speeds, and most definetly will loose E faster due to its poor acceleration compared to the spit. At high speeds the p51 turns exceptionally well. So does the P47.
Short of implying cheating, the move you described cant have be pulled off as you thought it was. It defies physics (virtual physics at least).
As for the N1k/Hellocopter they're great at hangin on the prop. Im not sure if what i can do is correct or not, but most people underestimate the nik, cause they think its just a slow turn and burner. Fact is its a very powerfull late-war monster with 4 cannons which can turn very well too. I treat them with alot of caution.