I have the '05 450x and my girlfriend has the '06 250x (Calif. models). I am 5'11, 180 and I am slightly faster on the 250x at the practice track at Prarie City. The 250 makes good power but you do have to rev it, not nearly the grunt of the 450 at the bottom. The 450 has very smooth power and is easy to ride. I was surprised how light the 450 feels compared to my WR426.