Brad there is another way to go, if you have the money and want to part with it!
If you want to use the steppers, and have the assurance of total accuracy, well within limits, look at the CNCBrain. You will need the Brain, encoders for your motors or a way to get them in the motion of the motors, and some linear scales. These can be expensive or you can build your own, which is what I am going to have to do due to the size of my machine. By using both types of encoders you can get a dual loop feedback with position correction, even with steppers.
The Brain is still in beta and there is not a lot going on with it right at them moment, but that is about to change. There is a forum for it on the CNCZone so just do a search. While you are at it you can do a net search for Safeguardrobotics....dot com I think.
Mike