the ratios (number of teeth) are of less concern than the DIAMETER of the "spur" (Pinion gear). The linear speed of the pinon is PI (3.1416) times the DP of the pinon gear.
Here is some quick math:
A 1" pinon moves 3.14 inches per rev...in essence a 3:1 STEP UP. That buys you 3 times the speed (about 1800 IPM off a direct coupled stepper) but costs you 2/3's of your torque and resolution. Since you start out with .005 per step resolution that carves it down to .015 per step. Coupled with the other errors (backlash, flex, etc) your accuracy will be less than .030
I know it's everybody's goal to build the cheapest table they can, but if you end up with a machine that won't do it's intended job then you have wasted your money.
The drive kit you listed is not a bad value at that price but beware that those drives are based on an older chip that is limited in speed and current and has no input isolation. It also offers none of the features you will need for plasma and you are on your own to deal with the noise and ground loop issues.
TOM CAUDLE
www.CandCNC.com