VPI Speed Controller

I had the very old PLC (Power Line Conditioner, the one with the thumb wheel dials) with my TNT-1.
I've upgraded that twice in the last 30 years - first to the PLC with the rotary dials and then to the SDS with the push button adjustment.
If you actually have an old PLC the SDS will be a very worthwhile improvement.
Still have my old TNT with various VPI upgrades. I sold off my Graham Phantom arm and put on a Grace G-1040 arm that I bought for about $150 in 1982. It actually sounds really good!
http://www.tobespages.info/TNT_grace1040._%20small.jpg

Been happy with my SDS.      Something to consider, if you haven't already:     https://www.youtube.com/watch?reload=9&v=AHmYWT3wKqs

Other posts are correct, the SDS is better than the newer ADS.  The ADS is cheaply made and has been the subject of many complaints.

However, you seem to be aiming for high performance.  If you want the very best, SOTA sells a motor-controller-roadrunner combo.for VPI tables.  It has been discussed at length in the VPI forum.

Other ways of improving performance would be the motor-flywheel combo, if they still offer it, and the peripheral weight.

@ joeyfed55-    To be more concise:  Here's something to consider, regarding the VPI Prime's maintenance, if you haven't already:    https://www.youtube.com/watch?reload=9&v=AHmYWT3wKqs    Happy listening! 

@rodman99999

That was a very  funny video.  Putting oil in the top of the pulley to lube the bearing.  Who is that moron?  He certainly doesn't know anything about turntables or motors.
Agree with the other posters.  Keep your SDS.