I'd recommend the GTX 970.
http

/www.techpowerup.com/reviews/NVIDIA/GeForce_GTX_980_SLI/
At 1440p (even though it specifically isn't listed), you should be just fine. At this time the 980 is the only better card, and it is only marginally better. You would pick up a few more FPS, and I don't find that worth the additional cost.
If you can wait, wait. There are rumors of a 980ti, and 8GB models for later in the year, closer to November.