My last card was a XFX DD 7950. Running 1440p via DP, gaming at a decent frame rate required setting pretty much every setting to Medium. I'd imagine 4k would require setting everything as low as possible to get any sort of decent rates. DX12 did give me a decent boost in performance on that card, but I still don't know that it'd be great at 4k. They're cheap right now if you want to look in to picking up a second.