Is it possible for SS to drive a servo motor at a speed greater than the nameplate RPM, without raising the voltage?

Ozzie

A servos rpm is proportional to voltage. I don't think the motor would last long, if you provided more voltage than it's rated for. I've read that you really should design to run at 80% of the rated rpm.

The Smoothstepper just sends step and dir signals, and can only have it go as fast as you have your motor tuning set.