A user on AVSforum is reporting 60hz 4k with a GTX980 on the 70" P-series!
http://www.avsforum.com/forum/166-lcd-flat-panel-displays/1689258-official-2014-vizio-p-series-owner-s-thread-70.html#post27770905
For what it's worth, it looks like the MSI GTX 970 4G (which is the highest rated 970 at this point) is now showing HDMI 2.0 on their spec sheet:
http://us.msi.com/product/vga/GTX-970-GAMING-4G.html#hero-specification
At least it says 1.4/2.0 - apparently from what I've read, the chips are...