OK, I've tried the side loaded Stadia app this morning, it has the know issues with it being slow to browse your games with the odd crash.
I connected a xbox one controller via Bluetooth and ran on 5ghz WiFi. I will do ethernet later.
The games launched and played at 1080p with no glitches. Response times on the controller are what I expected, totally playable.
However 60fps games looked more like 50fps for some reason. Not sure why, could be a app issue or the box. I pressed as/d button and it says I'm running at 4k60 so does the TV.
I tried gforce now and got a 60fps no problem with no input lag, however I have studdering audio.
I will try again with ethernet later.