[timstephens24]

I just tested mine, and here's what I found (needed to reboot each time I set the resolution - also no HDR for Netflix):
4k2k-60hz = Netflix 4k / No HDR
4k2k-24hz = Netflix 1080p / No HDR
4k2k-smtpe = Netflix 1080p / No HDR / Aspect ratio was screwy

While I was testing this I also tested out the speeds from an ethernet adapter vs 802.11AC and here are the results of three tests (using the Netflix app - I couldn't find a speed test TV app)
USB 3.0 Ethernet adapter: 41.33Mbps / 43.95Mbps / 42.43Mbps
802.11AC: 69.30Mbps / 63.84Mbps / 63.25Mbps

Also I decided to watch an episode of Luke Cage on each connection and with the ethernet USB I'd get some buffering issues (it would drop to 720p/1080p) that didn't happen on AC.

And just to second what @seymourtv said, disable the 'XiaomiLeanbackCustomizer' app.