Interesting, the rev D screen print says "15, 30, 60, 120" and the following article says
quote "And thanks to the InPort chip, the Microsoft Bus Mouse can be programmed for 30-, 50-, 100-, or 200-Hz operation. " so it seems there are differences between the revs. It appears the rate refers to how often changes interrupts the CPU and as the article explains it is possible to poll the board at even higher frequencies or hook into a vsync interrupt to adjust the cursor between frames. Great scan Al, it has all I need.