Other thing to consider is a possible/likely dual GPU from nVidia. Dual 970 like GPU would give you a lot of options if you wanted more power. *If* it gets release you could check in with two of those and or one of those plus a 970.
4k needs tons of horsepower, I'd put 970SLI at minimum for it and if you have the right mainboard definately consider notching up to 970Tri-SLI or better.
Personally excited for this as option for 4kHD on a big screen (60"+), particularly with the HDMI 2.0 support in the 970/980. Given I ran 290 xfire in my setup, I could likely get away with 970 Dual GPU and a 970 on my z87 board.