The reason gaming across 2 monitors, is a bad idea, is the bezel will be right down the center of the action. If you want to use multiple monitors, you'll want 3, not 2.
And many articles have been done on the subject of 3 monitor gaming, and more than 2 GB has never shown beneficial when the using playable settings, unless mods are concerned. (I figured you'd want that info, maybe you don't care?)