I found a neuroscience paper (quick google search) that states "we revealed that FS neurons in human association cortices (mostly temporal) could generate APs at a maximal mean frequency (Fmean) of 338 Hz and a maximal instantaneous frequency (Finst) of 453 Hz, and they increase with age."
Grain of salt and all that, but keep in mind that would be Neurons, I think the eyes themselves might be even slower. No way panel refresh rates of 600hz+ would be visually noticeable.
Someone correct me if im wrong.