Probably not very well. Currently running 5760x1080 3 monitor on my GTX 770 4GB, on medium I average 40 fps, using 3 GB of vRam.
Most games I run at medium to high graphics and I average about 3 to 3.5GB of vRam, at 40 FPS, so I use adaptive Vsync, and get pretty smooth performance. My rig has no bottle necks, its a intel i5 3570k OC'ed to 4.1GHz, 8 GB of ddr 3 1600, dual channel, with a ssd.
I still get some studder and feel any less gpu and vram would make it unplayable.
verified, just put my son's 2gb 770 in my mobo, UNPLAYABLE! studdered and was awful, did get um to play by lowering game settings to min. but looked awfull!
also got um to work by lowering res to 3840x720, but still looked bad