[Uoppi]

Talguy, I've never used madVR's zoom for that specific purpose because I prefer to maintain the aspect ratio but madVR's zoom settings have an option to detect and zoom black bars away completely (named "If big black bars are detected" or something like that).

For what I use madVR's zoom functionality, I can say it's quite versatile and works well. I haven't needed to touch Kodi's zoom.