Those are all factory overclocked, of course the 680 is the best, but is it really worth the extra 100 bucks? The 670 and the 7970 are almost the same. I plan on doing a triple monitor setup, my PSU will be the 1000W XFX 80+ Platinum and the CPU, will be the i7 2600k. And one last question, which one is the most future proof?
With a triple monitor setup, you will bring any of those cards to their knees. You need to SLI or CF. I'd recommend you CF a couple 7950's. Only cost $300 each and when overclocked they are as powerful as a 680 so for $600 you have about the equivalent of two 680's.
If you want a 670 from EVGA, get the ftw. Or I would say go with the msi 670 pe. For triple moniter setup, you would need 2 of those. But if you can't get 2, then get the amd since it performs better at anything higher than 1080p
I would go with the red team for multi monitor gaming. They have a better track history. If you must go with a single card, get a 7970 GHZ edition. Like others have said though, for three LCD gaming, you may need a dual gpu set up and I never recommend those.