Neither the 970 nor the 1060, IMHO.
The 1070 does well @ 1440p at mostly very high ro ultra @ 60 FPS in msot games, while you can probably get closer to 1800p or so at mediun/high quality settings at 60 FPS in most games.
That would be my entry point for "4K" TV gaming. That is, a picture that will look more detailed and crisper on a 4K TV at usual TV viewing distances over 1080p, while not necessarily being native 4K.
Lots of games are including in-game resolution scalers, dynamic resolution support, sparse/checkerboard rendering options, etc, so hopefully, most games will be easy to tailor to a good level fo image quality and performance on PC for 4K TV gaming and at 60 FPS on something like a 1070.
IF you absolutley must have full 4K (and I would relaly only personally insist on this if playing ona 4K monitor, not a TV fromt he couch, then you ar elooking at the 1080 or 1080ti if you want 60 FPS, and even then you might have to compromise some graphics settings down from very high to high or medium. Native 4K is brutal, especially on anything with a lot of per pixel effects and that doesn't feature optimizations like dynamic resolution or checkerboard rendering.
But if you are willign to compromise graphics settings ot console levels, you should eb able to get 4K or close to it at 60 FPS on most titles with a 1070 or better.