I have an SP-10MKIII. Technics claims: The inertia moment of the 10kg platter is of 1,1 ton/cm2... The platter has a 1,5cm copper alloy core (inner platter), supported by a diecast aluminium outer platter.
1,1 ton/cm2 is, BTW, the equivalent of 1000 tonearms all tracking at 2g.