I'm going to take your advice (all the advice seems consistent) about getting more horses in the stable. I never even looked at 3-phase motors, even though I knew they were cheaper in the large sizes, because I have only single-phase 220V. Am I reading correctly the controller will provide 3-phase to the motor from single-phase source?
Having said that, I've never loaded the grinder down significantly with the coarser grits when I'm leaning into it pretty good. With the fine grits, I learned not to put too much pressure on the blade or I get hot spots and warps.
Bottom line, if my old one-pony motor can be rewound cheaply, I'll keep it. If the price gets up there too high, I'll junk it and go with a variable speed controller and bigger motor.
Come on tax refund