Id probably say as of right now, Tonyjoey is the best in the p51. He's the only one I see who consistently lands 8+more kills at one time in the p51. Not to mention hes a pretty good stick in the DA too.
Steve was pretty good, Oldemon was pretty good, Skatsr was good, I mean it's a p51 for christ sakes.
It's an easy mode plane, that has a decent turn rate but I woudn't be cought turn fighting someone who was good in a N1k or F4U.
Pretty much the plane is best for BnZ guys who like to run and extend all the time after they miss their initial shot.
I don't fly it often because I do not liking running, and most of the time, a spit, N1K, f4u, ki84, hurr, 109,sometimes a p47m def 11, yak, will always beat it in a turn/stall fight. The plane is exactly realistic as far as WW2, it's fast, dives great, decent acceleration, catch it in the climb its toast, catch it trying to stall fight, generally its toast.
arguing who is the best in a p51 is like arguing who is the best at Picking and running in the game.