Parece un tema de drivers, en el foro de SB hay gente con tu tarjeta que no tiene problemas:
I use 7970 with 3 screens - so far I didnt had any issue with playing, but then it is not SLI , it is just game forced to run on that resolution. Everything is on max - shadows dont licker as well, just tested it with new drivers. As for F5 on 2nd screen - i tried that with running 2 games, but i could not manage them to find each other on my lan . SO now one of monitors is used for JPG image of actual map ( just terrain map, no units update, i get used to it, and it is kind of more realistic), along with mils table for arty