I've got an LG OLED (C8). It's freaking amazing. You have not seen perfect black levels or contrast until you've seen an OLED.
The Technicolor mode and HDR are
LG's also ship with Dolby Vision and the other HDR standards unlike Samsung which usually picks one.
As far as 4k > 8k goes, we've just arrived at the point that 4k content is readily available. Unless you get a screen that's larger than 55 inch I don't think you'll gain much from 8k.
If you can find one cheap, get an LG OLED now.
Also if you are in Japan I imagine you like animu. OLED 4K is like perfect for animu with a kick-ass upscaler.
Games too btw, fucking amazing how good something as BOTW looks which doesn't even run at 4k.
At 4k on Xbox One X everything looks stunning. Tomb Raider, Assassin's Creed, Ace Combat 7