As a former multimedia engineer, I know what a lot of the reviewers are talking about.
Especially when it was between 720p and 1080i, there was fertile ground for debate in that with 720p, you get 720 lines of information per frame whereas with 1080i you only got 540 lines of information per frame.
So for sports, there were many cases where the 720p actually had a better picture.
Moreover, the quality of the materials used ESPECIALLY the light source(s) made a much bigger difference than the line differential.
going from 1080p to 4k, which is actually only 2k because the resolution is 3840 pixels × 2160 lines as compared to the 1080 lines that comprise HD, is HUGE.
Even upsampled Blu-Rays look substantially better.
My mom got the curved 65" Samsung 4k tv when it came out and watching streamed 4k content (the only thing at the time was House of Cards) was as big a difference as the jump from 480 or a good tube tv to 1080p.
A lot of that has to do with better light sourcing, be it OLED or better LED source(s) and/or more zones of lighting. They also have intelligent pixels that do some pretty amazing things with the light to control light bleed which leads to deeper blacks which in turn leads to substantially better dynamic contrast ratio.
When the 4k TV came out, I wondered how long it would take for content to make the TV relevant.
Two seconds after watching it, it was clear that EVERYTHING including old I Love Lucy reruns made the TV relevant.
The nice thing about having a 4k Blu-Ray is that you'll be looking at native 4k content, so there's no chance for experiencing the artifacting that can come with any kind of upsampling.
And honestly, you're looking at a bigger TV. I can't imagine it's less than 50" and probably bigger.
Lastly, I call total BS on the industry's viewing guidelines. From a personal and professional standpoint, I think the "standard viewing" guidelines are so outdated as to be laughable.
"I'm sitting 10 feet away and this 85" tv looks too big..." said no one ever. Heck, there are home theater setups where they have a 120" screen and the first row of chairs is maybe 8 feet away. And I can assure you that when it comes to sports, people will get as close as they can no matter the size. Lots of things lead to that.
The ONE thing I would advise is to try and match the Blu-Ray player with the TV (unless it's a Vizio. They make decent monitors, but I wouldn't trust their electronics just yet). The reason I say that is because the algorithms will be compatible. It's less of an issue than it was during the early DVD days, but occasionally a person will pair, say, a Samsung TV with a Sony Blu-Ray player and have issues that while subtle are noticeable. That almost never happens if you use the same vendor for tv and Blu-ray player.
Plus...you can likely use 1 remote to manage both devices which is nice.
