GTX 660 or 670

the Vram on the gtx 670 assuming that it would be higher would do better on a multi screen setup. But I ask, did you purposefully not decide on an AMD alternative? AMD is more concrete with higher resolutions and multi screens because of the fact that Eyefinity has been able to work on a single card build for a long time now, as Nvidia is pretty new to having 1 card display several screens because originally, it would require 2 cards in SLI to do so.