It will be enough for a fair while, though some higher end games are already starting to use more than 2GB at 1080p. I'v seen Crysis 3 use more than 2GB on my rig.
Why do you have dual cards for a single 1080p display? (that your actually gaming on)
Thats pretty overkill, you would be better saving yourself $200 and just getting a single 780, which also gets you that 3GB of VRAM.