For a given 5- 6- or 8-wire (unipolar) motor used with a bipolar drive you can get higher step rate by using only 1/2 of each winding. But you will have lower torque at low to medium step rates which is where the cutting is done.
So... you have to trade higher inches per minute (ipm) and lighter cuts at the tool against lower ipm and heavier cuts at the tool.
In most jobs a LOT of time is spent moving the tool from place to place on the workpiece, so you are better off with the higher speed / lighter cut approach. In other words bipolar is better - most of the time
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robotic regards,
Tom