there are 3 standard trackball sizes I know of - 4", 3", 2 1/2". Maxi, midi, mini.
From what I understand of the MC cursor speed debate, it came about because they made different speeds to accommodate different trackballs for different cabs. But I believe they were standard, in other words, upright always had x size, cockpit always had y size, etc. Roy used a different speed, which was intended for a different sized ball, (the different size balls and different speeds should make the trackball move the same speed or feel that way at least. All the MC cabs I've played on or seen have the large size trackball. That large ball is hard to move but also allows more control than the mini. Obviously the 3" is the best design lol