I have been reading the advantages of Unipolar and Bipolar steppers and I have a hypothetical question.

If Bipolar steppers are better for cutting because of torque and Unipolar steppers are better for speed, couldn't a controller be designed to switch between the two modes using a Unipolar stepper?

It seems like a simple problem from a programmers point of view. If the spindle is lifted from the work, run unipolar.