It depends on what kind of games you're playing. A 770 won't run AC4 on max settings at a constant 60 fps even @ 1080p. The 770 is more than sufficient for most games, but the 780 or the 780 Ti will help bridge the gap in the rest of them. I just got a 780 Ti today (which replaced my 770) and I'm doing 1080p gaming as well, running two monitors, gaming on one, and I loved my 770. Served me very well. But the 780 Ti is just an animal in comparison. But yeah, if you're just playing standard MMOs, or like.. even Battlefield 4/Bioshock Infinite, a 770 will easily run those games on max settings with 60+ fps (BF4 will occasionally drop into the mid to high 50s range if you're standing in a big explosion or a ton of particle effects, etc). The 780 Ti just pushes those to the extreme. Was getting a constant 110+ on BF4 earlier, occasionally around 130-150.
TL;DR: If you can swing it, get the 780 Ti. If not, the 770 will still be a great card.