The problem with the comparison, is that FPS is not the only metric. When in SLI or Crossfire, you will not get as good of an experience at the same FPS a single card does due to double latency and inconsistent frame times. Add in that many games don't work with both cards on launch or ever and you have to make a decision on what point SLI/Crossfire is actually better than a single card. My guess, based on 1st hand experience, that you'd want 40-50% better FPS on an SLI/Crossfire setup before you choose it over a single card alternative. You still have higher latency, but you get more points of input to off set that to some degree, and the added FPS should smooth out the frame time inconsistencies enough to be worth it.
A 980 SLI setup is not 40-50% faster than a Titan X, so I'd go with the Titan X between those two. The 295x2 is a more interesting offer, due to it being a lot cheaper and provides higher FPS than the Titan X. But that becomes a value choice, rather than which is best.