Certainly grab a new GPU if you desire better performance in your games. Your CPU, even though a bit old, will certainly hum along just fine with a higher performing GPU. However, mind that when many players are on screen you will experience lagg. I experience lagg myself with my GTX 670 and i5-3570 (a great deal more powerful hardware than you got atm.) in Planetside 2 during tense situations.
The R9 290 has better value compared to the GTX 780, performing equally, yet having a lower price tag. If you were to step up the resolution, the R9 290 would even outperform the GTX 780 due to its high memory bandwidth as well as 4 GB of VRAM. I myself, even though a Nvidia fan, would grab the R9 290 myself if I were to choose.
I wouldn't play the waiting game and wait for the next gen, unless a date was confirmed. Technology will keep updating all the time, it's about getting the best you can for your money at the current time.