VPI SDS or Powerplant for speed control?

I have a VPI Aries table and use the PS Audio P600 Powerplant for turntable speed control and line conditioning. Recently at my VPI dealer and he states the SDS is superior in both areas to the powerplant. Spoke with PS Audio and their opinion is that they both work well and there is no real benefit using the SDS over the P600. Does anyone have have any experience and recommendation with these two products?