VPI ADS Versus SDS

Gents:

Has anyone "upgraded" from the SDS to the ADS? I've had a two VPI tables over the past decade and have always thought about but never tried one of their speed controllers. I'd be interested in hearing from folks who have used both models and can share comparisons. I've noticed that despite the introduction of the ADS there has not been a significant price drop of the SDS on the used market, which leads me to wonder whether the ADS offers a significant increase in performance. Also, I had heard that VPI was going to launch several ADS models but it seems there is only one currently available. Anyone know about plans for other cheaper or more expensive versions?

In general, what can you expect when you add a speed controller (either model) to your analogue playback system?

Thanks!