Just sharing my experience, I have directly compared a basic Rockport Capella II (ruby bearing, non-vacuum platter) with the 6000 airbearing arm, to a highly modified slate plinth Lenco with PTP 5 kit and Jeremy’s bearing (so pretty close to the PTP Solid 12 mentioned by Marc), and the Terminator airbearing arm.
On macro dynamics alone, the modified Lenco really had the upper hand, and it seemed to have even better macro dynamic than direct drive like the Exclusive P3a. The only direct drive that I have auditioned that could rival the modified Lenco on this area maybe the Technics SP10MK3 (but I have not done any direct comparison between them).
However, what it lags behind, as compared to other high grade belt drives and direct drives, are the finesse, micro dynamics, sound staging and layering of instruments within the sound stage. That could be due to the unavoidable higher vibration transfer from idler drive.
To answer Peter’s question, in my experience, the modified Lenco had very good bass quantity, but not quality.