gtx 780 Single card 1440p?

It will do quite well with slightly older games. I just upgraded to a 1440p screen myself a few months ago and my EVGA 780 SC has handled Mass Effect 3, Crysis, Crysis Warhead and Crysis 2, Sniper Elite 2, Dragon Age Origins and Dragon Age II quite well. It will not do so well with the newest, most demanding games though. The newest stuff will be playable but not maxed out.
 
My 780 cant max out the latest games at 1080p and keep 60fps so at 1440p it would struggle a lot more but dropping the settings would definitely keep things playable. My big issue is the 3gb VRAM, Advanced Warefare cant be maxed out at 1080p due to needing over 3gb vram even though I have enough horsepower (with a strong OC). GTA V is another game that needs more than 3gb at 1080p on the higher settings.

I reckon the 780 will serve you well if you are willing to turn down settings and be happy with frame drops to 40fps in some games.
 
Even a GTX 980 won't max the latest and greatest games at 1440p. 980 Ti or Titan X are about it. I'm thinking about buying a 980 Ti but I'm going to wait and see how the new AMD cards do first. Hopefully they will cause an Nvidia price drop if nothing else. $800+ ( probably ) for a GTX 980 Ti is just insane.
 
Gaming wise the original titan is no better than 780. Only go for titan if you strictly needs double precision in your application. Instead of titan you better of with 780 6GB model. Anyway if you need something purely for gaming wait for a few days and see how 980ti pans out. It will have 6GB as standard. Speculated price from 650-800
 
Im running SLI EVGA ACX superclocked 780's atm with the rog swift 1440p monitor. a alot of games are fine but there are some demanding games that i cant run maxed out with out having fps in the 30's, and that with or without slight stuttering depending on the game. when thats the case i usually drop a couple of things till i at least get an average of 50fps.

for example, i get witcher 3 running between 40 -70 fps and thats with most things on ultra, but antialiasing off, foliage render on v.high, shadows v.high, pop render v.high.
couple of odd small stutters here and there but mostly smooth.

im actually thinking about whether i should upgrade to the 980 ti now because i can see that these days, the games are starting to go beyond my cards at 1440p.

 
It's the 3GB VRAM limitation. If you had the 6GB versions of the 780 I suspect you would be fine. Those cards were always expensive though.