I can't believe I never thought of that--using multiple Tilemap instances to fill in the gaps. And it's not like using more than one Tilemap instance is foreign to me; I've done that in my Advance Wars Engine for Fog of War.
I dunno how I'm not getting your FPS. I'm getting 32 without reduced screen flicker and 25 with it on. Using RGSS104E, same map, same [1024, 576] resolution. Not a huge deal, but just puzzled.
If people want only a custom resolution script, I'd recommend this one. Not sure why you are crediting F0 and me since there is nothing similar between the two scripts at all (and it's not like that was the only resolution script that exists to begin with).
And yay, using the Alt+Enter discovery~