Hello again friends,

I observed and tested following problem:
in nVidia driver settings, G-Sync set-up, if it's enabled for windowed and full screen applications, then TotalMix FX by default does cause monitor refresh rate fluctuation (around 30-50fps);
at first I thought I got a faulty monitor, but after enabling on-screen framerate counter in monitor menu, I could clearly see framerate numbers jumping like crazy once TotalMixFX is the active window on top;

there are 2 solutions right now:
1) change G-Sync settings to "full screen mode" only
2) add custom rule (in nVidia 3D Settings) for individual program, TotalMix FX - that is located in C:\Windows\System32\TotalMixFX.exe and adjust setting called "Monitor Technology" to "Fixed Refresh" (default global is G-SYNC there), tricky part is to quit and relaunch TotalMix to immediately see changes

if this could be somehow worked better into TotalMix FX directly somehow, it would make life a bit easier