Cr 125 need some thoughts?

i want a cr 125. Im 5' 10" and 160 lbs. How fast will it go with me, and how much power/acceleration. I wanted to get a cr 250 and ride it eady untill i get good, but i hear you really need to ride them hard to keep the plugs from fouling. If i get a cr 250 can i ride it easy and work up or will it flip me and kill me. And dont forget will a cr 125 go fast/accelerate/power well with me. Yhis is my first dirtbike and all i have driven has been a mini bike.