ill have 2 monitors at 1920x1080 and one at 1280x720
i guess my next question would be which is the best 7970?
Wait so you plan to use surround/crossfire with those 3 monitors? or do you only game on one? If you plan on using those 3 your resolution would only be 3840x720 and at that resolution I would go with the 670. If you get another 1080p monitor the memory bandwidth/vram MIGHT be an issue and then i would go with a 7970.
(from my experience nvidia cards are slightly "smoother" than the amds but that might just be me.)
Ok well if you plan to use the card on 5760x1080 the extra vram and bandwidth would be helpful on the 7970, so go with that and like others said you can just get a cheaper 7970 with decent cooling and OC it you don't need to pay the extra for a ghz model.