A GTX680 is still a beast of a card and will handle most anything at 2560x1440 at max settings. Crysis 3 and one or two of the most demanding games out there might be a little too much for max settings though at that resolution.
If you can swing it, a R9 290, R9 290x or GTX780 would be a worthwhile upgrade if youre going to that resolution. Youll be fine with our current rig and still get great performance in most all games out there but if youre wanting to max everything and get all the eye candy you can, then youre gonna need to shell out some more bones for a GPU upgrade.
AMD FX 8350 @ 4.815 - 1.40V CnQ enabled
EVGA GTX 670 FTW @ 1070 (1239 boost)
Asus Sabertooth 990FX rev 1
Corsair Vengeance 1600MHz 8GB
Samsung 840 Evo 250GB SSD
Western Digital Blue 1TB x2
EVGA Supernova G2 750
HP 2509B @ 1920x1080
Corsair Carbide 500R
BlackWidow Ultimate & DeathAdder