Up to post #29 GTX 770 was never an option. You asked about GTX 970 and R9 390 in previous posts. This is the reason that it looked like a typo when, out of the blue, you mentioned GTX 770 price.
In any case, do not even consider a GTX 770, taking into account it's price and what card you currently have.
By keeping your HD 7970 card for another year, you will lose $140 from it's resale value.
Getting a GTX 970 for $400 now would mean that if you can sell it in a year for $260 then you would have used it "for free" instead of your HD 7970 (same $140 price loss). Even a smaller than $260 resale price (bigger loss) would be compensated by the fact that you used the GTX 970 and enjoyed it's better performance for a year.
And if the new generation is delayed or disappointing, you can still keep your GTX 970 after one year.