Current best GPU for 4K HDR 60FPS Video Playback

[Erenke]

Now that there is stuff like Stadia coming out, what's the best GPU for 4K HDR 60FPS video playback.

 

I'm asking this because if we consider Stadia becomes the next big thing (unlike OnLive and Nvidia thing), many people will cut the budget for the GPU since they won't need it too much. I would rather build a computer with a powerful CPU and less powerful GPU rather than balancing them if I would have an option like Stadia.