Hello Paul,
I have solved the speed problem with the addition of a used PS Audio P-300. It stabilizes the voltage provided to the motor, $400. I wound up getting the 300RPM motor as well, which helped. I tried converting to string drive, but gave that up, the smaller diameter string changes the speed, so you would have to go with the SDS to use it.
This setup works very well for me. I agree with you about proper isolation, it has worked wonders. To better this would require much more money to be spent, I believe.
Enjoy,
Dan