Man, hang on to your 780Ti until the new Nvidia cards come out. With a card like that there is very little reason to upgrade with a new generation coming out very soon. Likely what you pay for a card now, will get you significantly better performance in 6 months either from the new generation or a better model on the current generation.
Your 780Ti outperforms my overclocked 7950 and I run at Med/High 1080P like a champ with 16GB DDR3, SSD, and a Haswell 3.4ghz i5. You should be able to run at 1440P on medium settings just fine with that card and system specs. If not, and you can tolerate 1080P it would run even better.
It just doesn't make sense to upgrade right now, IMO.