Using the data that you have provided, which doesn't say what type of micro stepping you are using, or what voltage the PS is. I guessed at 10 micro steps( which I justed checked and is NOT one of the options) x 200 steps/ rev x 10 tpi = 20000 steps/ per inch. Insert what you are using for micro steps in the formula.
The only way to find the fastest speed that your machine can reliably go is thru trial and error. Try this for starters. 20,000steps per inch x 10ipm = 200,000/min or 333.333 per second or ten ipm. I forget how it is setup in Mach3 and I don't have Mach3 in front of me. If the motors are actually stalling, you willl hear a noise that will make you cringe, it is an ugly buzzing sound. If you are failing to return to zero by only .020" or so, you may have play in the system that you need to correct.
If it is off buy a huge amount say 1" plus, then you are in for some real fun. One way to make sure that you are not loosing steps is to make a mark on the stepper motor shaft and then run the code. When you get back to the starting point, the mark should be exactly where it started.
The 10tpi acme screws will limit you on fast you can ultimetly go, but as long as it is fast enough for you, then that is OK. If the motor can turn 500 rpm and not loose steps, your max carriage speed will be 50ipm. For some driver and motor combinations, 500 rpm is not possible. Similar motors on my Taig mill at ~30v will only go 10 ipm on a 20tpi screw which would be 20 ipm on a 10 tpi screw. HOWEVER I am not using the keling drivers and Your Mileage may vary.