They are right, not even the 125 will be under powered but, my first bike was a 1981 RM 125. I rode it till I blew the motor up, didnt own another bike for over 12 years, but rode various 125 and 250 2 strokes. Then a buddy of mine got a 2004 Yamaha YZ 450F, I rode it and WOW!, 2 weeks later I went and bought a Suzuki RMZ 450. So I am pretty much a beginner on a 450, there may be more maintainance envolved, but its not a whole lot more, besides its kinda fun to do. I will never have any desire for any 2 smoke ever. Thumpers are the way to go. Check your valves every 15 hours or so, change your oil religiosly and your air filter as often, like every other ride and you will be ok, you will never need performance parts for new 4 stroke 250's or 450's, they will always be fast enough. I never need all the power my 450 has, but its cool to have it there. 4 strokes rule!