ViperTX, he gets 1" of travel for every 1/pi revs of the motor.

dowling, your calculations looks correct to me. Kevin's suggestion of 9:1 ratio is probably due to the fact that it can be achieved with two 3:1 timing belt reductions (i.e. relatively easy to do). If you get enough force with this ratio, then just limit your motors to 600 RPM, or enjoy some 380 IPM rapids! Otherwise, perhaps you can find a planetary gearbox with a higher ratio on Ebay, for example.

There's no particular reason to use the same ratio on different axes, other than that perhaps it's easier to build several similar reductions.

Arvid