honestly man, i'd go for whatever you think you would really get more use out of...i am 5'6 148 lbs. and i bought a brand new 04' cr85 expert (same size as the kx100) 2 summers ago, i was about an inch shorter then i am now then, and i was looking at the same options, either an 85, 100, or 125, i picked the 85 expert cause it's the same as the 100 size wise, but i just like honda, and how the bike felt. I thought i would be to uncomfortable on a 125, so i'd wait a little, and just settle for something smaller. I tore it up on the 85, and i still fit it fine and i have a blast. I mean, it is easier to control, being smaller and all, but the 125 will be the same after awhile of getting use to it. Try them both out, and think more of the future, either way man, good luck, and you can either raise or lower the suspension on either bikes....