Dear Dertonearm, I hate to harp on this issue, but I have a "thing" about bad science, such as your contention that the mass of the slate is a major determinant of the distance that a billiard ball will travel (and your bogus reason for saying so). I have done some reading on the physics of billiards, as a result of my consternation. Two things emerge from my research: (1) Once the ball is struck, the major contribution of the table to the distance and direction in which it travels is the static and rolling friction between the ball and the felt, as I surmised in the first place, and (2) slate is used for billiard tables not for its high mass per unit volume but because it can be worked to achieve a very flat surface, and once made flat, the surface of slate is very stable as regards humidity and temperature, i.e., it does not warp. Here I offer a reference to a pretty nice article I found on the internet that reviews the Newtonian mechanics of billiards:
http://archive.ncsa.illinois.edu/Classes/MATH198/townsend/math.html
Now if you can concede that your metaphor is ill chosen, perhaps we can also open our minds to re-examine the idea that platter mass is the sine qua non of the highest end turntables. If I could find an article that addressed your other bald statements, that a certain platter mass is needed, regardless of the drive system, and that the dynamic mass of the Saskia platter does not count as "mass", I would post those too. I don't have the requisite experience to disagree; I just don't think you have the "data", even of the subjective kind, to back up those two notions. The only defendable fact here is that YOUR turntable, which is a belt drive of a certain type and construction, sounded best with a platter of a certain minimum (high) mass when auditioned by you and your colleagues. (I don't know whether you made measurements of frequency response or speed stability that could be adduced to strengthen your case as regards your turntable, but if you did, I would be interested to see same. I am assuming your conclusions are based on subjective listening tests.) Now I can go bang my head against the wall, because my favorite football team just once again pulled defeat from the jaws of victory.