thanks for testing, comparing to latest madvr beta (which I only just upgraded to and which brings it own blackscreen problems with some discs for me) and using your settings from avs for that, madvr is retains rather more saturation these days. I haven't noticed brightness instability that I can recall though, any other scenes noticed that on? I don't have max max so can't compare that one.
The black screen with some discs with madVR might be because you have the measurements files enabled in madVR settings (configuration / files and folders) and have old measurements files for these titles. Recent test versions don't support measurements files, which causes these black screens when some are present. Delete the measurement files if present, or to be sure check "ignore all measurement files" in madVR configuration settings.
Re brightness jumps with JRVR, try any high nits films (mastered to 4,000nits or more) with fast scene changes. Maybe Pacific Rim, The Meg... The bathroom scene in chapter 4 of MI6: Fallout can be a good test for that too. So are the conference room scenes with Morgan Freeman in Lucy. I've stopped using JRVR since I noticed this, as it's a dealbreaker for me, so I don't have other example. But when madVR has some brightness stability issues, the above are the clips I use to test and eradicate.
There are no stability issues with the settings I posted recently on AVS for madVR (it definitely needs details threshold at one and either Mars or Mercury, as well as doubling the default brightness speed adjustment settings, and conservative contrast settings (up to log low or log very low max). Indeed, there is a lot more saturation and picture depth than JRVR, and no brightness stability issue.