trying to figure out the way to have none of the non-sync judder with all the benefits of high refresh displays. at 72fps you can either run 144 half refresh vsync,which imo works very well but is prone to losing fluidity if the fps is inconsistent or you can run g-sync/freesync on,judder free experience regardless of framerate, but you lose the benefit of higher motion clarity that 144hz provides would double refresh g-sync work ? let's say 65-70fps at 130-140hz ?
Gsync I doubt (you'd need to fool the display somehow into double refresh rate) but you can set a fixed refresh rate at e.g. 120 Hz and cap the framerate at 60 with Vsync on. As long as refresh rate is an exact multiple of framerate there shouldn't be stutter. The display just shows the same frame two (or three or...) times. Btw this double sync is exactly what LFC is actually, when under the VRR range the display will set refresh rate double of frame rate, like 70 Hz at 35 fps.
