HDR makes a bigger impact on things than 4k. I didn't go the OLED route this time around for a number of reasons - but my Sony XE93 with that beautiful 1000 nits brightness with HDR makes things come alive. When you see those contrasts between the blackest blacks and brightest brights.
I've experienced both HDR10 and Dolby Vision (the latter with something like Altered Carbon is just something amazing).
This is with streamed sources and PS4 Pro gaming, so god only knows how stunning it would be if I have a UHD player.