Sli 760 4gb vs single card. 1440p monitor

[LOA5000]

Hello I am looking to upgrade my GPU. I have the gtx 680 2gb rite now. And i might be buelding an extra pc so i can just put the 680 in that. I rite now with the 680 when i play battlefield 3 it uses all the vram so i am looking for more vram.

Looking to play battlefield 4






My set up is
Amd 8350
Crosshair 850 Watt psu Gold
X hauf Case
H100 CPU water cooler
Amd 990 V formula mother board
8gb Ram 2133
250gb ssd
1tb Hard Drive
Asus 2560x1440 27 5ms monitor

 

[LOA5000]

so looking at getting the sli 760 set up 4gb or single gtx 770. The 780 only has 3gb of ram