I wasn't sure if you were seeing this all the time or not until you mentioned being in a gaming session. Often the various antianstropic and other settings may have to be tweaked just right if not disabled or left on automatic to get things running smoothly.

If I had the extra desktop space here I wouldn't mind having a 3rd monitor in use! At times that would be a plus when having several browser windows open even! The price tags are still a bit high however for one brand of triple monitor setups. Triple Monitor Multi Screen Display | CineMassive Trio

If your board is SLI capable that would be a thought to boost up the vpu power a bit. Plus you would then have a second card to drive the 3rd lcd with.

With the dual monitor setup here I use either UltraMon or DisplayFusion. For adding on a third lcd then I would be looking at other programs like 9X Media for one option. Unfortunately none of these programs themselves will stretch any pc game across more then one display unless the game itself has that type of option already included.