My frames do not drop below 80 fps and run at around 140 fps.
as for lowering visuals.. I\m running an RTX 2080.
cpu on this sytem is a Ryzen 1700x But i\m experiencing the same on intell cpus.
BTW: I was looking at some FRAPs Frame Timing data for my system [2.2.5 / no mods]. I'm not sure if this is what you're seeing but I'm getting roughly 200 milli-second periods of time where my frame rate drops well under 20 FPS and then things go back to 60 FPS. Are you seeing something vaguely similar? How often do you see that?
Tried some other games and the others I've tried appear to be much smoother in terms of consistent FPS / Frame Timing / Average FPS close to "max" FPS / etc.
Note: I've got my system locked to max of 60 FPS as that's "good enough for me" most of the time.