Hey Robert,
did you already use the search function and searched for Lower speed high torque spindles? I ask because among some relevant threads on the topic, there was this thread the other day:
Note that the assumption that a spindle with four magnetic poles which runs at half the speed of a spindle with two magnetic poles will automatically have twice the torque has not proven to be true, if you follow this thread.
(It is however true when comparing e.g. 2-pole HFS-8022-24-ER20 (0.9 Nm constant torque from 6,000 – 24,000 rpm) to 4-pole HFPM-8022-24-ER20 (1.6 Nm constant torque from 3,000 – 12,000 rpm))
You remember also the thread Cutting thin gauge steel which you participated in.