Choosing the right bike has as much to do with skill as it does with size. A beginner, on a 250 2-stroke, that loses his balence and falls backwards causing the throttle to twist will head for the woods at mach-10 doing a wheelie into the trees. A beginner on a 125 2-stroke that does the same thing will head for the woods, but only at mach-3 and maybe not wheelieing. I know this from experience, I'm now back on a 125 and having more fun because I'm more in control. I also weigh 225 and my new YZ125 has no problem pulling me around. A 125 takes more work to make it go fast, slipping the clutch and shifting, but put a fast rider on a 125 2-stroke and he will whip the average guy on a 450 4-stroke. My point is that it is more about the skill of the rider than the size of the bike. I also tried the CRF250 4-stroke for a while this year and found it much easier to ride due to the great low end torque but I didn't like the heavy, bulky feel as compared to a 125.