Depends, what are you really playing right now? If you're playing a lot of the newer games like Watch_Doges, AssGreedUnity, CoD: KevinSpacey Warfare, and the likes of those and want to play games like GTA5, The Witcher 3 and etc then the jump from the R9-280X to the GTX 970 is WORTH IT. You will see anywhere from a 5 to 30 FPS jump in performance.
Now if your cup of tea is like WoW, Hearthstone, CS:GO, Diablo III, Starcraft 2, etc that are a) Slightly older or b) slightly lower in requirements then hold off. For games like those the R9-280X is still fine and it might be better to wait till next year to see if nvidia rolls out a new line or Ti's everything.