TitanX is an truly epic card, but for the same money you can buy a pair of 980's then all of a sudden its a very difficult decision.
Titan X really is a 4k gaming product in my view as you will never get stutter from running out of VRAM as right now I do not think there is a single game on the market than can use up the full VRAM buffer maxed out.
So if you have a 4k monitor a Titan X all the way and a pair of them would be amazing for 4k gaming. We've had a few customers today actually buy 4 Titans for themselves, quad Titan SLI, BOOOOOOOOOM.
But a pair of 980's now looks like great value.