I figure the only way to have early war planes fighting in a competitive environment would be to have a seperate "early war arena".
What I want to know is; who would be interested in flying in such an arena often, and also, which planes should be in an "early war arena" ?
IMO...
The top end would be planes like the Bf 109E-4, P-40B, Yak-1, Spitfire Mk I etc.
Later fighters that were low on performance would be allowed too, eg: CA-12 Boomerang, FM-2 etc.
At the bottom end would be the biplane and early monoplane fighters, eg: CR.42, Gladiator, I-153, I-16, Ki-27, P-36, G.50 etc.