@danaos75 This sounds like what I experience .. sorry I don't have much further to add, in terms of a solution. I just try to reduce frame-rate such that adding 7ms time won't cause a missed/late frame.
Also, I gave up on g-sync .. I just run 60hz fixed-refresh rate now. Variable refresh sounds nice in theory, but in practice, to my eyes, I find an occasional skipped frame is less jarring than seeing a frame rendered out-of-phase with all the others, once a second.
I do fly with Windows 10 "fullscreen optimizations" enabled. (I measure it saves 1 frame of input-lag, when running borderless-window with overlays present. I don't recall it having any effect on the micro-stutter experience, though.)
My older quad-core rig is at a different location, so it may be a while before I can test on it.
But yes, for quad-core systems I recommend doing the affinity-mask thing, to run BMS on cores #1-3 (leaving core #0 free for OS, DWM, graphics driver, audio, input and networking etc).
Hopefully 4.36 will be available soon, and we can start our testing over, from scratch. :P