Having owned and ridden several '90-02 RM, YZ, KX, CR and KTM's I can tell you power hasn't changed dramatically since the powervalve motors came into play. If you could see a dyno test of a new CR125 and CR250, I doubt there is even a 2-3 peak hp difference (remember it weighs 20lbs less so power to weight?). You just have to keep the 125 spinning. This requires a lot of clutch movement<--which will require more maintenence. I weigh around 260lbs so I notice this a lot more than you would. My last 125, '91RM, would pull 4th gear wheelies with me on it. My last 250, '95CR, would pull 5th gear with a lot of help due to the fact that its power would come on lower and keep pulling.
The largest downfall to a 125 is resale. 125's do not even hold the value that compareable 250's do. My personal choice would be a new 200 or 300exc KTM. They are pricey but come with the best of everything. The 300 has the same hp as a CR250 but have a little wider powerband and more torque. Plus, I haven't owned a KTM yet![img]i/expressions/face-icon-small-smile.gif[/img]