The thing about 4K is that you need a lot of graphics horsepower to utilize it properly. I have an i7 CPU that's overclocked from 3.4GHz to 4.3GHz.
I'm using two 3GB R9-280X OC GPUs in crossfire with it.
The system runs on SSD drives, so it's optimal in a lot of ways.
With all of this, I can't game at 4K with the eye-candy turned up.
Maybe the new R9-390X will be able to do it, but I suspect it will take two of those to manage high 4K framerates in demanding games.
It's an expensive proposition.