What would perform better for gaming in a single screen? I've seen people have said go for the better Graphics Card rather than SLI of two lesser ones, but I'm still left wondering.
Yes but tri sli of a 680 is about the same power as quad sli of 690. It is also considerably cheaper. So, I would suggest going with 2 x 680 as you can then add another. Also, if you are gaming on multiple screens, 2 x 4GB 680 will be better than one 4GB 690 (It is actually 2GB) because of the more VRAM. You can four way sli 680s but it's pointless. So few games make any use of quad sli or four way sli that it's not worth it. tri sli is doable, cheaper than quad sli and will provide an alright improvement.