Bill, I was responding to your comment "You cant possibly compare the YZ 125D with the RM 125B" - maybe not in 1977, but you can in 2010.
Donny's bike has YZ250D forks and a longer shock - it gobbles up the rough stuff like a stocker can't and the motor's power curve is a lot fuller than the RM's (although I'm sure it lacks the peak HP figure of the RM). The more of a wobbler you are, the more it helps.
And your trolling skillz need work - MX-C vs YZ-X is arguing that more weight, less power, crapper suspension and a(n even) more flexy swing arm is better?
Davey, you're on drugs - unless the RM is made out of helium? The YZ-D is considerably heavier, for sure - but the C/X is a damn light bike. Seeing as none of us are the 60kg jockeys that the bikes were designed for, a few kilos here or there is pretty much just pissing in the wind if the rest of it works well.