SL-1200G/Hana ML Best Headshell

Think of it this way: square root of 9 is 3. Square root of 12 is ~3.4. So the difference between 9g and 12g is not going to affect the calculation of Fr by much.

Should have noted that when you multiply effective mass times compliance and take the square root, keeping compliance constant, then the ratio of the result with a 9g vs 12g effective mass is even less different than the square roots of the two numbers 12 and 9 would suggest.

As regards the SL1200G or GR tonearm(s), if the headshell weighs 7.6g, which is light as headshells go, then the total effective mass of the tonearm in question would very likely be greater than 9g, it seems to me. More like 12g.

The tested effective mass of the GR tonearm is the best actual data I have seen for this spec and the G arm should be very close to this number. 

Effective mass as spec'd for tonearms is a qualification of its inertia or resistance to motion, not the weight of the arm wand.  The most influential properties that affect the inertia are headshell mass (same for G and GR),  distance from headshell to pivot (same), counterweight mass (same) and distance from counterweight to pivot (same).  Bearing friction is also a factor and assumed to be the same. 

The Gs arm wand is made of magnesium which is lighter than aluminum but again not much of a factor in calculating effective mass.  The EM of the GR and G should be nearly identical.