[hannes69]

@ashlar
Nice explanation of the target refresh rate! Please correct the typo "Target refresh rate = 23.97602 * 0.9999758 = 23.79544" in order to not confuse the people even more
Would be cool if you could explain in such a short compact practical oriented manner the second part of the story concerning the custom refresh rates (I´m not very good in explaining things SHORT

Clearly madVR OSD is displaying the "corrected" deviation numbers, not the actual clock deviation"

No. Madshi (the author of madvr) explains himself the story about the clocks here, glad I found it.

the deviation continues rushing past what it was supposedly stabilized at before, then gradually slowing down again and setting at a notably different percentage.
What's more, I get different deviation percentages with different 23.976 movies. The difference can be as large as 0.04%.

There seems something odd in your setup, that´s definitely not the normal behavior. There are small variations (because of heat, electronic effects...) but not that huge. Maybe worth a try to look at the BIOS setting regarding HPET support, this may influence the clocks. No other idea beside that.