1" Mount to a 2" mount... 8x the mass on average. double each dimension. There is a turnover point where the mass just gets out of control. That's about at a 2" mount.
My 1.5 " head weighs about 65lbs without counterweight. My 1" head weighs about 20 lbs.
I believe you on the mass multiplier factor. I'm using the 2" bearings for an equatorial fork mount. Pretty standard polar axis but the fork will probably be composite construction, with small stub shafts for DEC, and possibly only 1" dia.
I think 1-1/2" shafts is the biggest I'll go with one of these GEMs unless I build that observatory one day.