The standard 3-phase, 60Hz motor has two pole-pairs (x 3 phase x 2 poles gives 12 segments or slots). The speed control consideration can vary depending on the motor design, application, cost, efficiency, life time, power factor, etc. Presently, the major factor is the suitability of a motor for variable speed drives; essentially to be able to dissipate the heat from motor losses (R square I) and the heat caused by harmonic currents (Eddy Currents). Manufacturers tend to classify these motors as variable speed drive motors or inverter motors.  The larger motor manufacturer tech support has the motor and motor drive alignments readily available. Some of those alignments come as one unit.