Very unusual ground performance despite a displayed 60+ FPS

Agreed! Most people don’t realize if you have your monitors refresh rate set to 120Hz and no fps cap, your GPU will work to push out 120fps. Setting vsync (or capping fps at the driver level) to say 50% of your 120Hz monitors refresh rate locks it at 60fps and allows you to now increase the eye candy and still have stable game play with minimal stutters.

I’ve also noticed if your monitors refresh rate setting in Windows has smidge smaller refresh rate than what you originally chose, select the smaller refresh rate. The sim will run slightly more smoother - see pic below with refresh rates circled in red.