Not sure that even a single 7970 would throw pixels well for gaming at that resolution. I would go with a dual 7850 setup and see how that works.
As for Eyefinity I will leave that to the experts here. I personally do not run multicard setups but that is a personal choice. I find that it was to hit and miss with game support meaning I often only got use of half my purchase. That has changed in recent titles however so it should be less of an issue.