A lot will depend on how much friction you have on your lead screw and slides, I have found that using a reduction gear before the lead screw is often better when using thread bar. Like with anything homemade, it is hard to predict your exact needs without a bit of experimenting. The best thing I can suggest is to get an old stepper from a printer/photocopier etc. and try it out. if you have some pictures of your Gantry please post them so we might have a better idea. goodluck and have fun!!