Ok, to answer the original thread question after the necessary clearing up which yak-9, the first, was intended.
This the P-39 wins hands down, sorry to say, but the facts supports it.
To go by the raw performance numbers (I think it was Corsning that supplied those upthread) theP-39 N has a clear advantage, but let's add real life context.
The first Yak 9, obviously being the prototype, will when the P-39 eventually arrives in the USSR supposedly be much the worse for wear. It may still have the ability to fly straight and level, but considering that most kills are scored against enemies obliviously puttering steadily away and never see it coming, theP-39 exceedingly well documented total inability to fly straight and level will stand the unveary pilot in good steed. Imagine the frustration of a Luftwaffe pilot upon seeing his intended target, even when unsuspecting, somersaulting all over the sky and stubbornly refusing to stay in the gunsight for any appreciable amount of time. Anyway it will not be worth the bother, as the total unpredictability and confusion as to whether this is one of the P-39 that actually carried enough fuel to land the aircraft, will deny him any surety of a kill, as even if he manages to get a burst in its general direction, probability is it just dropped out of the sky on its own accord.
As for the late war Yak 9 with functioning uprated engine, raw performance should make it the winner, though. I know of no-body... make that I know of only one, who would ever claim a 1943 P-39 to be superior to the latest front line fighters of spring 1945.
I apologize in advance for posting this now, but even though the thread - being a P-39 thread - expectedly still will be active then, I have not the patience to wait until 1st. of April 2022 before posting it.