I have a friend that has a 2000 YZ 125 and he fits it nicely. He pulls a ton of power and weighs 180, so I think you are probably good. He did add an extra bit of fork oil though to stiffen the forks (he was bottoming out a bit.) He likes the light-weight feeling of the 125 more than he likes the power of the 250.
Another friend has a 1999 CR 250R. I jumped on that thing and I will agree with you, they have mucho power. Another guy has a 98 and its nice as well. I ride a 97 KX 250, and it feels like the CR's pull better to me. =]