If he isn't gaming on the 3 screens, a 2GB version would be just fine. Also, most cards do not have 3 separate hdmi connections but in the 760's case, two dvi to hdmi adapters will work just fine. There is no loss in image quality. Only thing I think lost would be audio which wouldn't make sense to have anyways.
I myself run 3 screens off my 670 2GB, and it works great even for heavy loads like gaming.
I myself run 3 screens off my 670 2GB, and it works great even for heavy loads like gaming.