A 980Ti or a pair of 970's in SLI would work. A 980 would be pushing it.
You could look at it this way, three 1920x1080 monitors only has 25% less pixels than a single 4K monitor. Most benchmarks place the average 980Ti FPS at 4K between 35-45 FPS, so adding 25% would yeild an average FPS at 5760x1080 around 44-56 FPS. Granted this is only a general ballpark estimate, but should give you a general idea on what a 980Ti would be able to do at that resolution.