Question Bad performance below monitor's refresh rate


Feb 1, 2014
Here's my configuration:

i5 6600K overclocked to 4,5 ghz with aftermarket heatsink
Newly bought RTX 2060 Super
16 GB of Ram
144hz Acer G-Sync monitor

I had just replaced my of 660 GT videocard, but I noticed some nasty low performance visual effects everytime the frame rate goes below 144 fps (my native refrsh rate).
Basically, even if I get a respectable 100 fps (or 110, or 80, generally everything slightly below 144 fps) the result looks like the game is running at sub 60 fps, with a really nasty effect.

I tried fiddling with G-sync, V-sync, anything, it just won't work. I am trying to play some old games like Starcraft 2 and Sudden Strike 4 and the scrolling lag is unbearable.
Same results on newer games like Chivalry 2.

Basically, unless the game I play runs at 144 fps or very slightly lower, I get horrible performance like the game is running at 30 fps, despite the fps counter reporting 80-100.

Video drivers are updated.
I tried removing the cpu overclock, zero results.
CPU temps are well below 60 celsius, even with overclock and cpu at 100% load.
Monitor is correctly set to 144 hz and Gsync is enabled in both fullscreen and windowed mode, according to nvidia panel.

What do you think is wrong?