I'm looking to build a new rig here, and I'm a bit stuck on GPU choices here (should this go into the graphics section?). I would prefer to use just one 1080p monitor (probably 120Hz) and I'm looking for a high-end gpu configuration involving SLI/CrossFire. I have a pretty decent budget for the whole build ($3500), so I can probably accommodate most configurations, but I just wanted to know which set up would be most effective in terms of 670 vs 680 vs 7970 (Ghz) and whether SLI/CrossFire is actually worth it. I'd like to play FPS games at high/ultra video settings, and I'd like to know the best way to go about doing it.
Finally, for future-proofing, is 3Gb more worthwhile, and could you also recommend a suitable PSU wattage for such a GPU configuration (Ie. would I need more than 850W?).