Because windings are better utilized, bipolar stepper motors are more powerful than a unipolar motors of the same weight (usually by 50%).
Performance of stepper motors are highly dependent on the driving circuitry. Torque curves may be enhanced if the polarity of windings can be reversed more quickly. The limiting factor is the winding inductance. To overcome this problem, driving voltage must be increased, but current limiting circuitry must be implemented in order to protect the motor from high current this increased voltage can induce.