Jonathan, I'm viewing a 6400. There is pwm if you use an external camera(mobile) to film. It appears below backlight 9/10, I have brightness on -5 and contrast on 90 for general use. That's still pretty bright. I'm still experimenting with light lamps to brighten the room/desk space. Also with the settings on the tv from this topic and a youtube video mentioned in this topic.
I'm on a 1070 and not playing any recent AAA, so no idea on high, but older games, homeworld2 is big!
I am though seeing a slight viewing angle colour shift. As I slump, which prompts me to sit back up straight. The monitor for me is a bit low, so I have it up on some books till i decide to strip my other monitor off it's arm. Iv'e come from dual 2515's to through a 3415uw. I do software dev and a bit of other stuff. If I grid the screen into quarters it's like the old days of 4 19" monitors. I also have a x230 which is prone to pwm and I know I 'suffer' it. The x230 won't do the 4k screen, it will drive the UW though...
Do I prefer it to the UW... maybe. Still adjusting to it's dimensions. I think I'm honestly laying out my windows in the top 1500px area, the lower area, i.e. the bit not on an UW I'm putting ancillary console/test/reference materials, so not actively watching all the screen. I guess it's great to have I can push stuff away, but still have it. That said I also like single 'panel' focus, so code and console only feels pretty big, but very sharp and easy to view.
I've also pushed it back as far as I dare over the edge of my desk. To the point I'm not moving my head, just my eyes. I'm also a screen use glasses wearer, but have found I've not needed to reach for them quite as often as I did before. But the screen is now an extra 6" inches away...
Is it worth it? Prime 4k kicking back with a beer, yes... 8+hours a day developing code, not so sure, but I'm kind of saying yes, if I can tame the brightness. If not then when santa is done in january sales it might get paired with a console.
HTH.