Download and install the latest version of "PowerStrip" by Entech of Taiwan.
This is the best video utility ever made, and one of its 12,713 features is the creation of custom resolutions for any video card on the market.
Also use it to force the refresh rate (No more "Reforce" required) at your chosen resolutions, fix the screen geometry completely, remember icon positions (for when you flip resolutions) and lots of other real good stuff too.
Then read my dissertation about frame rates, and setting up your PC for gaming goodness. http://planetdescent.com/d3help/framerate.shtml