No not at all they will perform wonderfully, my preference would have been to go with two 7970's because of the Vram and 384 bus. The incredibly low power draw from the 670's are a big plus however. A lot of games use FXAA and soon maybe TXAA so wont require much memory. Back to the point you are SLI'ing two monsters you will be fine for a long time.
Thank you for putting any fears I had to rest.
I guess I can mark this as solved since my initial concerns were the compatability of using mixed monitors in an Nvidia surround setup. I'll most likely purchase 3 of the same monitors.