When I press the Home remote button, the screen is 720p50, never knew that. And as I don't know of any other source of 720p50 (BBC iPlayer always seems to be 720p25 and the YouTube 720p videos I've looked at were also 720p25) I don't think that there is a reason to select a setting of 720p.
The switch between resolutions isn't seemless, so going between 576i and 1080i results in a whiteish screen for a second.
SD (576i) seems worse when upscaled to 1080p by my Panny plasma compared with the V6, quite surprised at that. It just goes to show that you need to do some experimenting to find what your equipment is good at.
You have a 4K TV, so everything displayed will be at 2160p50. If you want the V6 to upscale everything, just select a video output setting of 2160p. But what if you want your TV to do upscaling? For starters you should select 1080p 24/25/30fps and 2160p 24/25/30fps, meaning that anything at these resolutions get passed through to your TV. Most videos you play on Netflix should be 23.976 frames per second (annoying and commonly and wrongly called 24fps), so a Netflix video at 1080p23.976 should get passed through to your TV if VM just leaves it alone.
Note that you'll still need the 2160p setting as a "catch all", e.g. just in case Netlix streams something at 59.940fps (happens sometimes in the US, don't know about the UK). So, try this for Netflix: