turntable speed control

SDS is better as once you set a speed it is locked to that. Phoenix corrects speed so it would be constantly changing which could be audible. 

The best belt would be a endless rubberized steel cable style belt like the old micro seikis. Quiet and they can't stretch. Micro did things right

If the motor on the sds system is always turning the same speed the platter will not go faster because the bearing is warm. That's a load of hooey. And I think the affects of belt creep are also greatly exaggerated. You could always go to tape, silk, or thread if you are concerned about that. To me a a constant stable speed is always better than a changing one.