How Well Do Late-Model 4K TVs Upscale Signals

We are planning to buy a 2018 model OLED TV within the next month or two - LG or Sony.

I'm interested to know how well these tellies upscale ordinary broadcast signals from the FTA channels and Sky - i.e SD and 1080p. There's a lot of info and comment on the internet about this but it's non-specific and does not necessarily relate to NZ conditions.

I'm keen to hear from people who actually own and use late-model 4K TVs under real, on-the-ground Kiwi conditions.