To run a second display at full tilt as a single you'll need to double your GPU horsepower. It's not a matter of CPU power as you read http://forums.cnet.com/7726-19687_102-5378367.html
Bob
Hey can you guys help me out im having computer trouble. Today i setup a second monitor on my computer i have been meaning to do so for awhile now. But when i got it setup everything on the screen has a lag to it and when i try to play games with it setup there is a lag. Im using a Intel Hd graphics 4600 for my first monitor connected with a hdm1 and the second one is connected straight to my nvidia geforce gtx 760 ti Oem with a DVI cable. My computer is a i-7 processor and 16 gb ram. So it should be more then enough to run and my drivers are up to date. Please helparino.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic