I bought a 4K TV
It's a Sony KD-55X9000E, which in America is an X900E or in Europe an XE90. The first thing I did was set up the PS4 and enable HDR, put GT Sport in the slot and did a lap of the 'Ring in the late afternoon.
It was eye-meltingly pleasing.
I have only a standard PS4 and honestly the picture is clear enough at 1080p for me to not worry about 4K right now (although I have seen God and it was a God of War clip on YouTube at 4K). I'm just happy with the HDR representation, as that was the whole point in buying this screen. I was skeptical about HDR at first, but then I got an iPhone X and was completely sold on the tech. But the big benefit in HDR is not how bright things can get, it's about how near-perfectly black the blacks can get, and watching favourite movies like Star Wars (which have lots of black in space scenes, coupled with the letterboxing) will be excellent.
And right now I'm downloading a 1.6GB firmware update. For a TV. It really is the future.