In the past i had 1 hd7970 running on 3 24'' monitors and i also had manny problems with fps drop with a couple of games. (call of duty MW3, Kane and Lynch 2, Syndicate) so I contacted the service desk of AMD but they couldn't really help me. The problem i got with the card was that i had FPS drop. And i think its because of the bad drivers from AMD so i returned the card and got back to nvidia and i don't have anny problems with nvidia surround.
Maby your card is bad ( manufacturing defect) or maby you have to wait for new drivers. Try to contact AMD maby they have a solution.
Try
this forum to explain your problem maby they can help.
Good luck!
Sh4dowking