The 980 is far from a 25% improvement in performance. More like 10%, if you're lucky. I wouldn't recommend it to anyone at the current price. 970 all day.
I know I'm not helping any but I've been torn on which to purchase also. I've been reading every post/review/blog/article I can find trying to find that very answer. One review I read that was helpful with BF4 was:
OC 970 FPS @ 1080p was 87.5
OC 980 FPS @ 1080p was 98.3
OC 970 FPS @ 1440p was 58
OC 980 FPS @ 1440p was 65.5
Basically it looks like so far that there is a 7-11 FPS different between the 970 and 980. But that is of course dependent on the cards OC. Thinking out loud here, because I need to write down the obvious, the 970 OC is close if not equal to the 980 stock. Just have to wait and see what differences will come with driver updates. I'm also curious if the power balancing feature of the 980 will make any difference...