In other words if you are struggling to maintain a smooth 30 fps turning PhysX on high might make your experience noticeably worse because it makes it just that more difficult to maintain that smooth 30 fps, and ANY performance degradation will be significant and make your experience less pleasant. If you’re not running a video solution that’s already struggling, turning off PhysX won’t make much of a difference.
Modern Nvidia graphics cards do not suffer much of a performance hit from PhysX - this is a tale told from old days, when it was true, that is no longer true.