GTX 1060 (3GB) + 440.82
nvidia-settings was sufficient to eliminate all tearing and didn't cause any manjor performance drop. Occasional stutter in desktop effects might have been present, but I'm not quite sure about that.
Games usually worked better with KDE compositor disabled, but were tearing-free.
RTX 2070 SUPER + 440.82
ForceFullCompositionPipeline causes ridiculous stuttering - even the mouse cursor is not moving smoothly. Disabling it removes this issue, but results in screen-tearing in most applications.
Tearing in desktop applications can be solved by enabling
TripleBuffer and disabling
export KWIN_TRIPLE_BUFFER=1 to
/etc/profile.d/kwin.sh and setting tearing prevention in compositor settings to "Re-use screen content".
It's not perfect, though, because it only has effect while the compositor is running, meaning that games will likely exhibit tearing.