I’ve got a couple of 4k LG sets and they both work very well with 4k content from PMS, so long as you do everything you can to avoid transcoding and get the fastest network connection between your TV and PMS host. For me, that means:
connect the TVs to the network using 5GHz wifi rather than the 100mb/s wired network (this may or not be your best option, depending on the strength of your wifi signal and how many neighbours interfere)
avoid TrueHD soundtracks, they don’t automatically fallback to ac3 and can’t be passed to your sound system over ARC and will trigger a transcode
DTS-HD MA or DTS are good audio options
don’t use bitmap subtitles like PGS, stick with SRT. The LG sets can display text subtitles without transcoding
ymmv, but I tend to choose reencoded movies over remuxes, as the bitrate is lower