if you are looking for a used bike go with a kx125. for new bike go with kx100. thats for racing. if you want a fast trail bike go with ktm 2 strokes. or kawasaki klx140. those are the fastest for you. those are nice 2 strokes,. 110 is wayyyy tooo small for u. 125 2-stroke is good!!! go to www.craigslist.com
dont get a two stroke i used to be a two stroke man myself but in recent times the two stroke has been overrun by these new four strokes nowdays a 125 two stroke will get beaten by a 250 four stroke thats why new motorcycling laws have allowed the 125 two strokes to be bored out to a 150 to make them even with the 250 four strokes also the four strokes are much easier to ride you dont need to hold them in there powerband to get them moving i rekon you should go for a 250f if racing motorcross go for the kawasaki kxf 250 they are a great bike and in the right hands can turn better lap times than a 450 f
but beware you will have to keep your maintainence up to a four stroke because if you blow them up they cost alot more to fix eg change the oil frequently clean the air filter after every days ride etc..
if you want fast then u want the 09 kx250f. this bike is said to be the 09 250f bike with the most oomph. its a seriously fast bike and loves to snap the throttle.