The changes made in the N were incorporated into the Q. They're essentially the same plane with the same performance and capabilities. The only (major) difference being the outboard guns. But this doesn't matter much since most Soviet pilots had those removed anyways.
I'd love to see the .30 outboard guns on the P-39Q in-game, just to fill-in for the M/N models. That, and I'd love to ping the heck outta folks after my taters are gone!