The gear indicator is an off the shelf design by Biketronix, they have been less than helpfull. I agree that 75Hz is slow, but I don't know how many pulses/rev are generated by the ECU.
I have asked other bikers forums about these displays non so far are positive. My plan was to experiment with a reduced frequency, to see if this had an effect. I have tried reducing the input voltage from a maximum of 10.5 volts, to 6 volts but this had zero effect on the point the display starts to display incorrect values ( a "n" for neutral).
I did try reducing and increasing the wheel speed pulses without effect.