technics 1200G tonearm effective mass 12 grams?

After extensive listening, I have come to the conclusion that the effective mass of the 1200G is lower than 12 grams.  As it still sounds great with MC cartridges, I am finding that its happiest with higher compliance MM cartridges of the past.  I cannot get over how good this old Pickering cartridge I have sounds with this arm as if it was made for the arm and table.  Has anyone else thought about this?  I bet that 10 inch arm on the flagship would be amazing with the flagship SP10R or 1000R with MM carts.  You could have the 10 inch technics for MM, the SME 3012 for SPU carts and the Fidelity Research FR64S for the MC carts like Koetsu and you would be set for life. lol.