You got 720p,1080p, 4k. More pixels. Doesnt take a fuckin brain genius to figure out if your tv's picture looks better because of course it does, and you don't gotta do anything to get it to work. but they realized that past 4k, shit ain't gonna look much better for the cost. so what do they do? more colors per pixel. only problem is color settings on tvs suck. tv manufactures handle this like dogshit. so now you gotta spend 30 minutes before watching a movie cause your fuckin tv automatically changes the setting from time to time for no fuckin reason. all this just to get slightly more colors. it's not even that noticeable. i fuckin hate HDR. i fuckin hate tv manufacturers.
the shining's still a beautiful movie but fuck me did i not notice the HDR one bit.
Captain Disillusion has a great video on the subject: https://www.youtube.com/watch?v=1unkluyh2Ks
For specific films you can google search but the long and short of it is that almost every single big budget film may or may not be shot at 4k or in imax but its always downscalled to a 2k pass simply because all the VFX passes are still rendered at 2k for the sake of render times. That 2k master is then re-upscalled to 4k for its final release. This process is pretty much standard and ubiquitous for all film releases which is exactly why 4k is such a load of fucking bullshit for film.
Something like Lawrence of Arabia depends ENTIRELY on the remastering/restoration process. For a crown jewel release like that the studio usually will front the cash for a full blown remaster of the original negative but just as often they'll cheap out and just upscale a 1080p master from several years ago and re-encode it. Sites like blu-ray.com usually do a good job keeping track of where the source files come from so they can advise the consumer on what double dip purchases (or downloads :) ) are worth it.
Three additional notes worth considering: -Often whether or not the original director is involved is a valid consideration in a 4k purchase. Some remasters are done without there involvement and they take....less care and/or creative liberties. The criterion release of Robocop versus its original bluray release is a perfect example.
-Some films may never get true/proper "4k" restorations/remasters simply because they can't. Star wars is one such tragedy. Film degrades over time and some chemical processes on films (especially from the 70s apparently) reduced the longevity by a massive factor. The original negative for Star Wars is apparently so far gone its basically lost to time at this point.
THE BIG ONE: -Your 4k remuxes are probably worth holding on to even still. 4k as a resolution may be pointless BUT the bitrate, color depth, and codecs still most likely makes those files superior to the bluray remuxes as a watching experience. Some Bluray masters still use Mpeg2 for gods sake.....