I've had a few 4k's turn up recently. Here's a summary. Audio setup is 7.1.4.
Alien and Aliens. The inside of the Nostromo really comes alive in 4k. The detail is striking. The audio of Aliens is the standout, really exercising all the speakers.
Dune Part 1 and 2. I'm not a particular fan of the story but Denis Villeneuve is such a great movie maker that I will always watch whatever he produces. The cinematography and soundtrack are just overwhelming. Magnificent.
Sicario and Sicario 2. Villeneuve again for the first. The soundtrack of the first movie could be used as a reference to test out your home theatre. Helicopters all around you in some scenes and bullets flying everywhere. The second is OK as a movie but not in the same league.
The Creator. John David Washington stars in this sci-fi story that must have kept the CGI guys busy for months. Not particularly engaging story but the visuals and audio are stunning.