There’s a “very high quality” option that can be unlocked by tinkering with some of the Xbox app’s configuration files.
To enable:
- Edit userconsoledata in the xbox app folder C:\Users\%USERNAME%\AppData\Local\Packages\Microsoft.XboxApp_~~~~~~\LocalState
- Change IsInternalPreview to true.
As others have noted it can overwhelm your network if you’re due for an upgrade…
https://www.reddit.com/r/xboxone/comments/3gq0pk/very_high_settings_in_xbox_streaming/