After I got the Eagle and RR, I tested my setup, (1) without the Eagle and RR, (2) with only the Eagle AC regeneration, and (3) with the Eagle/RR feedback correction.
What I found was that the stock motor (VPI Scout II) was inherently stable to
33.3RPM, just not to the 0.00 precision because of fluctuations in the
power coming from the wall. Adding the Eagle and its power
regeneration led to a steady 33.33RPM with a narrower fluctuation in
the 0.000 range, sometimes hitting 33.333RPM. So that proves the stock
motor runs properly when fed proper 60Hz power from the wall and when the motor is located
properly from the table. Connecting the Eagle/RR with feedback made the
fluctuation much more tighter in the 0.000 range, hitting
33.333RPM for longer periods of time. Audible? Depends on who you ask but I noticed a difference (not night and day, but identifiable) . YMMV.