You would need to figure out how much each axis weighs, how much force is needed to "push" each one, the speed you need to drivev the axis at cutting speed, and the drive ratio of each axis, plus some headroom (maybe about 10-15%) From there you should be able to deternine the "torque" you need to drive each axis. The torque ratings of different motor frame sizes can overlap. There are a few useful articles on the geckodrive.com website that you should read to get an idea of motor sizing as well as power supply sizing.