Harold, I have it installed on my Yamaha GT2000 stock tonearm which has an effective mass of 19g when taking into account the headshell. This is not considered ideal as I think would benefit a lighter tonearm.
I was going to install on my Audiomods tonearm which is only 10g and sits on an Oracle Delphi. Unfortunately the pins on the Level II are very thin and the cardas tonearm wire pins are too loose.
Therefore I have kept the F9 Ruby fitted to the Audiomods/ Oracle.
I have to say that even though the pairing of GT2000 and Level II is not supposed to be a good match on paper, it is breaking in very well and starting to wake up and already outperforms the Grace F9 Ruby.
As as for the top line Grace models, I think I have read that the F14 BR/MR is considered the top of the bunch with the Level II ceramic and F14 Ruby close seconds. But as you say, it all comes down to the rig one uses and personal preference.