You never know when the 700 series will get released though. For all we know they end up with some issues and keep delaying the release.
So if you are eager to start playing right now, i'd go for something they already sell, like hd7970 or gtx670/680
^ +1, remember upon release of the 770/780 you could possibly get two GTX 670's for the same price, which would no doubt cream a single 780. The next generation of cards (GTX 700 and Sea Islands), are just improvements on the current architecture. You will likely see around 15% improvements across the board, which isn't a whole deal. I would probably skip GTX 700's/HD8k and grab a Maxwell card or something in 2014.
The 7970 is pretty much the top card right now, prices on the new ones will be high, they may not be out for months, and a 7970 will last a few years anyway. It ALSO comes with crysis 3 and Bioshock infinity free if those interest you. Should both be great. I wouldn't worry to much about waiting if you want it now. Really its up to you.
Side note, an i7 is a waste of money for gaming, an i5 makes way more sense and performs the same. You might also want to get some memory
Depends on the display you have. The upcomming Titan is about $900 so that's not in your future. Perhaps the 8870, but that's due in Summer for perhaps 15% more graphics power, nothing to put on Facebook.