Incredibly, even our multi-GPU setups failed to deliver an average of 60fps when playing on ultra at 2560x1600, with the GTX 780 SLI cards topping our graph at 58fps. To which we should note that while AMD's GPUs currently have an edge in this title, Crossfire isn't scaling nearly as well as SLI. As a result, the HD 7970 GHz Edition cards averaged 51fps, while the 7990 was limited to 48fps. A single Radeon R9 290X averaged 39fps, matching a pair of R9 270X cards and outpacing the Titan by several frames.
If you plan to play at this resolution without multiple GPUs, you'll probably be stuck with high quality graphics instead of ultra if you want decent frame rates with your modern performance card.