For such a resolution 5760X, a single card is not sufficient unless you want to play the games with medium quality. @ 2560X resolution it give around 30-35 FPS in most intensive GPU games. So definitely you'll need to SLI it.
If you SLI the GTX 670, you get the same performance of GTX 690, so you might wanna have a look @ surround benches with GTX 690.
EDIT: Anyway here's a review showing the GTX 670 in surround http://www.bit-tech.net/hardware/2012/05/10/nvidia-geforce-gtx-670-2gb-review/6