You didn't mean O-ring chain did ya?.. Did I miss something? If you did mean O-ring chain I noticed a little bit of power loss running the O-Ring chain but they will last forever.
X type o-ring chain supposed to seal out dirt better and have lower fricton than standard o-ring chain. I know lots of guys that run o-ring chains on 125s.
I ran into the problem with my '02 YZ 125 that the o-ring chain wouldn't totally clear the case the pins would of rubbed into. Might just want to put like a washer in there to space it out alittle bit.