Ah an OLED set........ first technology to beat Plasma. Very nice purchase LG has the jump in this market... The ones that I have seen have pretty good up-converters... from 1080i/720p to native 4K (US broadcast is 1080i as are the cable feeds). So the standard content still looks better on your OLED. However, you really need 4K content or a 4K bluray to see the set perform.

Motion is the challenge for up-converting (It's why you don't see much sports on the sales video loops.... and a lot of what they package in there is in slo mo) Waves/sea state could be a really big challenge....versus the boat with defined edges etc .. It could be the OLED video processor just can't cut it. (its a lot of processing power)

It sounds like your set is defaulting to 720p. take a look in the setup to see if you can force one of the hdmi inputs to always up convert all content to 4K. The alternative would be to find a pre processor that your video card can run to convert your video and do the re scaling and up-converting process to the native 4K your set wants.

Sometimes they have a code in the video stream that toggles the up-conversion on. You would need to preprocess your video or have the set take control.

I envy your problem!!!