Already ordered two though mate, its for a 5760X1080 res set up.
You should have lead with this. Two 680's or 670's should be excellent. The resolution and refresh rate are what generally determine what video card setup you should use, assuming a reasonable CPU, which yours is.
4GB is not necessary and will make little difference for 5760X1080, kepler is limited by its bus width. Better off getting 2X 680 2GB instead. Your CPU can overclock a little higher, but should be just fine.