Quoted from Jam_Burglar:I suspect they put some effort into engineering the flipper lag issue and ended up around 5 ms because that's where it becomes nearly impossible for a person to perceive the lag.
I think Williams chose to poll at 4ms because that was the best the 6809 cpu could do without impacting other things. Whitestar had the same cpu but could do better since the DMD code was offloaded.
Had they had faster cpus I would think they would poll more often, just to reduce the variance.