Do a month of "Hanger Queens". You know, those planes that "suck" in the MA that you never see?
Either P-39.
I-16
I'd say Spit XIV but you said no spits.
Or
A month of "Elite planes that should be perked"
Brewster
Bf109K
Spit XVI (I know....)
P-51D
Why not fly something "beneath you" just as an experiment?
wrongway