Surely you would be better off selling the 2 7950's and getting a single 290x or 780.
Not really because the 7950's are averaging 120fps in BF4 at 1200x1920 full ultra which is much faster than a 290x or 780ti.
I was thinking with an "eye" for eyeinfinity to use 3x7950's which is precisely my brothers configuration (hes got a 3930k though) so was thinking of maybe an extra 280x or 7950.
A 290x can only produce circa 40fps in 4k so at 6k it might only produce 30fps in BF4 using custom ultra 4xmsaa. So it would need to be 2x290's/X's to hit fps mins of 60 IMO.