B/c the link is saying you wont notice a difference after a certain distance, something I thought was going to happen...so much so that I moved my couches closer before pushing them back to 8/9ft for room aesthetics. You will notice a 1080 to 4k difference but even when youre super close, 4k isnt mind blowing. HDR is the real difference.
However, a lot also depends on the quality of 1080 tv to 4k tv. My sharp was huge but the panel was shit...so moving to the LG was a HUGE difference.
If you already have a plasma, for example, you might not notice a huge jump in picture quality. For me, even at the distance Im at from the tv, 4k is noticeable for both gaming and movies (and even streaming). Its a much more clear and crisp picture. Hell, even cable being upscaled lookes great.
Heres a good example: I'm a home theater snob so I notice everything (good or bad). My buddy could give two shits. After setting everything up and helping me mount it on the wall, I flipped on cable (HBO) and Aliens was playing. Its an old movie. He was blown away by the picture quality and the upscaling. It looked like a modern movie. He continues to be blown away by both SDR and UHD content.
My point is, the distance thing is a general guide but definitely is a "your mileage will vary" type of thing.
Hopefully I didnt ramble.