Software? = Mach 3 - without a doubt. It's free for a fully working version, but is limited to 1000 lines of code and 25Khz step frequency in 'free' mode - $160 fixes those limitations if they are a problem. For many, these limits are not an issue.
I would look at the weight of the gantry and the rolling resistance of your guiding and possibly reconsider your 200OzIn motor selection - that seems a bit weak, but I could be off. I guess that depends on your accel and speed.