If you’re wanting flexible frame durations (not tied to the fixed 60 or 120Hz refresh of a standard monitor) you might want to think about the G-Sync system (nVidia or probably the similar FreeSync system of AMD).
A recent paper by Poth et al shows how to make G-Sync work in PsychoPy to give frame durations of exactly 4.5, 5.0, 5.5ms etc
It’s very neat! 