There is a good historical overview of the evolution of the SOTA tables in TAS Issue 210 (Feb. 2011), written by Paul Seydor. Concerning the speed stability issue, he has this to say:
The DC Papst motor, the one real bete noire of the early Sapphires, has long since been replaced by a superior high-grade AC synchronous motor. In older Sapphires the motor was mounted via an undamped metal plate to the plinth; in the new ones, a damped plate with rubber-encased well-nuts acts as a kind of shock absorber. Together these changes result in even greater speed constancy and retrieval of musical detail.
On my early model Sapphire, purchased in 1983 and still going strong without ever having been serviced(!) or upgraded, I've certainly noticed a slight speed instability at times (mainly on piano notes), which I've presumed is mainly due to "hunting" by the servo motor that was used in the early models. I have not found it to be severe enough to be significantly bothersome, though, so I've never seriously considered sending the table in for upgrade. YMMV.
On another note, one thing that never fails to amaze me about the table is that I can pound my fist on the plinth while a record is playing, with moderate force (I've never tried heavy force), without the slightest audible consequences. Try that with a Linn, or pretty much any other table that is in a similar price range! Actually, don't try that with a Linn :-)
Regards,
-- Al
