Your perception is absolutely real. With your monitor refresh set at 165Mhz and your in game vsync set to 50%, this will force your video card to work to achieve 82.5 fps. That’s a tall order for any system and hence you noticed only around 60 fps being actually achieved (and with a little stuttering).
By setting your monitors refresh rate at 85Mhz and setting in game vsync to 50% forced your video card to try to drive the sim at 42.5 fps which was well within its capabilities (with a little to spare). Since your video card was now more balanced with your sim settings and PC CPU, your perception of a greater sense of fluidity was the result.
I’m surprised a little that setting your refresh rate at 165Mhz and your in game vsync at 33% did not provide the same fluidity at 54 fps as that is still under the ~60 fps you were achieving previously. From what I have seen in the past, utilizing vsync based on the monitors native refresh rate seemed to work best. Was your in game resolution set to the monitors native resolution?
The bottom line is that you have achieved some balance all of us strive to find which is extremally difficult as no 2 PC’s are the same.