The shipping weight on my mill was over 1200lbs, with a spindly steel stand that a 60 year old man easily pressed over his head. 'Maybe' 150 lbs. Maybe. Not a cast iron stand that is added to the total machine weight and adds little rigidity. And no, it's not "just" a larger envelope. The castings are significantly larger (how else are you going to get a larger work envelope?) and very well webbed. The head to column interface on this mill has to be seen to be believed. I have run several different RF clones and the 12Z and IMO they don't compare. Others may or may not agree, but that's what opinions are made of. Other than coolidge, who else here has run a 12Z? Or are we just comparing spec sheets? That practice, as others here have pointed out, is dubious at best.
Not trying to convince anyone here of anything. Everyone is entitled to their opinions, but some are just a bit more informed than others. I'll say no more on the subject.