I have recently replaced my monitor setup, I used to have a setup of 1x 24" and 1x 17", but now I have 3x 27" 2560x1440 monitors. On the old setup, I ran games at 1920x1200 in borderless window / fullscreen windowed mode. This allowed for easy (&fast!) multitasking between game and desktop.
However with this new setup, to run fullscreen windowed, I'd be forced to run the games at 2560x1440 resolution, and that takes a major toll on the FPS. I'd like to run games in windowed mode (non-fullscreen) at 1920x1200 or 1920x1080 with black borders surrounding the non-gaming area to improve performance (i.e. same way fullscreen with lower resolution works on many monitors, but without the alt-tab delay which happens when changing resolution between desktop and game).
Running games in windowed mode is technically not a problem, the problem is that whatever is behind the game (i.e. my desktop/applications running in the background) is somewhat distracting me from the game.
TL;DR: Is there a good way to run games in windowed mode at resolutions less than a monitors maximum resolution, with black borders automatically applied?
I'm using Windows 7.