Hi, I hear your confussion. I have been riding for about two years, i started on a quad, but didn't ride very much, basically got the hang of changing gears, etc. I then bought a KDX200, when I first got it I really battled, as I wasn't used to 2-stroke power and I had never really ridden a 2 wheeler, well 3 months down the line and maybe 8 rides under the belt and bordom struk. I then spend huge money trying to get more power out of it and eventually after a year of riding it I finally got to the point, where there was know other way than getting a 250 2-stroke (kx250 2006 rules), best move I made and it is easier to ride than the KDX dispite having more power.
did I make a mistake getting the KDX, I don't know, I think if I did it again I would have just gone for the 250 2-stroke.
I weigh about 90kg's at 5'10" so I am a similar size/weight as you. remember it only goes as fast as you twist the throttle. But if I were you I would probally go for a KDX200, because you have had even less experience than I had when I started.