Speed accuracy- how accurate is accurate?

@OP

zavato 

Certainly, running at 33.333333333333 . . . with a stylus in the groove is ideal

Not if the Music itself has been recorded a bit slow or fast

What IS important is to have easy control to make your platter faster or slower and ensure it stays there when set. imo.
 
Now if the turntable does not have this type of control, given a choice between running a little slow or fast - definitely faster is better.  

In my opinion....

Pitch stability is MUCH MORE about off-center holes than variations in properly performing turntable motor operations.  The difference between 33.31 and 33.35 is insignificant as long as the speed remains relatively constant in the short term.  Unless a listener is absolutely pitch perfect (very tiny percentage of listeners), they won't know the difference in the long term.  Even cutting lathes didn't maintain perfectly stable speed rates.  (The Beatles "Golden slumber / Carry That Weight / The End" seriously changes pitch increasing from slightly flat to quite sharp during the recording, but it quite listenable.)

In my opinion, the REAL issue is not about speed accuracy for A/C driven turntable motors.  It is ALL about A/C noise making its way into the platter or plinth.  There is a quite noticeable difference in noise entering "the system" when the turntable drive motor A/C voltage (VPI Aries and VPI modified TNT) is reduced by a variac from 120v to around 75v.  That is still enough voltage to maintain stable platter rotation to operate the table but the vibration generated by the A/C synchronous is dramatically reduced.  This can further be demonstrated by using different kinds of drive belts.  Reducing this noise floor makes a big difference in detail, soundstage, image tightness, instrument character and performance subtleties.      

Just my opinion and personal observation (as a former professional performing musician).  Your opinion may differ, your opinion may differ.  

I think you and I have gone back and forth on this subject in the past. The issue with the voltage going to the turntable motor could be of two sorts. In one case the motor can directly radiate EMI which can affect the cartridge. This would mostly be a problem with direct drive turntables where the motor is installed right under the platter. In the second case, the AC interference from the motor goes back on the AC line and goes to your other components via The AC line. This latter problem can easily be avoided by isolating the AC supply to the turntable from the AC supply to your other components, particularly your phono stage, line stage, and amplifier. Reducing the AC voltage supply to the turntable by as much as you suggest, going from 120 V to 75 V, can have a deLeterious effect on the performance of some motors. Because at some point the torque will drop dramatically.

I also kind of disagree with the idea that the speed accuracy of the turntable needs only to be as good as that of the cutting lathe. Because if the turntable speed constancy is poor, then you are adding an additional source of error to the speed at which the record runs. This error in the turntable could be additive with the error of the cutting lathe, in which case you are losing some fidelity that would otherwise be obtainable.