I have to assemble a one hour loop for an output of 4k MP4 for a public display of art and the monitor is a QLED 4k LG. I know the answer is go 4k Pro Res HQ all the way,
I think we need to unravel this a bit so you can better understand both the replies and possibilities.
MP4 is generally a container, not a codec. It can contain several codecs, including H.264 and H.265(HEVC) variants, but there are others.
One bit of information is how the files are being played back, as that may impact the codec choices and quality.
Another bit of information is the source files and their codec(s).
I’m not sure what you mean by “go 4k Pro Res HQ.” Is this your request for the source file codec? Is this the codec you want to edit in?
As others have pointed out, editing involves recompressing and, before export, FCP defaults to ProRes 422 (not HQ), but you can certainly change that.
If you’re asking them to deliver video files to you for editing, you may need to consider how they’re capturing and generating those files. Do you want them to take on the responsibility of upscaling lower resolution files to 4k ProRes HQ if they are creating the files in another format?
Depending on how they’re playing back the files, newer playback systems should have no problem with HEVC 420 8-bit. Older systems might be better off with H.264 420 8Bit but that may require a higher bit rate to match the quality of HEVC. It’s possible to exceed the maximum bit rate of the playback device so it is important to know what they playback device can handle.
As you are aware of, the internet speed and file size can impact the time it takes to send files back and forth and that’s certainly a factor. If that’s a serious concern then HEVC is best file size to quality codec to work with. You’d need to know what their up/down internet speeds are and how much time they have to best judge that.