Really, both will do fine. I say the titan has the advantage with 6gb of vram. SLI'ing them will only give you 3gb of usage vram. (They don't stack) Unless you want to pay extra for 780 ti's at 1400-1600, seems like the titan would be a better choice. Plus 2 cards means SLI problems, and takes more power to run. Sure it'll be more powerful then the titan, but again, costs more and higher requirements.
IMO, 1 780 ti can run them with no problems.