...Displayport 1.2 is capped at 60Hz 2160p and DP 1.3 goes to 120Hz 2160p. But nothing is DisplayPort 1.3 yet, it just got finalized I believe. HDMI 1.4 is capped at 30Hz 2160p and 2.0 ups it to 60Hz 2160p. The 970/980s have DisplayPort 1.2 and HDMI 2.0 (http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-970/specifications), so the max you can do is 60Hz at 2160p.
Displayport 1.2 is capped at 60Hz 2160p and DP 1.3 goes to 120Hz 2160p. But nothing is DisplayPort 1.3 yet, it just got finalized I believe. HDMI 1.4 is capped at 30Hz 2160p and 2.0 ups it to 60Hz 2160p. The 970/980s have DisplayPort 1.2 and HDMI 2.0 (http://www.geforce.com/hardware/desktop-gpus/geforce-gtx-970/specifications), so the max you can do is 60Hz at 2160p.