I just bought a '96 XR250 about two months ago (I'm not exactly a novice...I've driven just about every other kind of toy). I love it!!! I'm also 16, but 6'2", 175lbs. I don't know about the weight difference between the two, but I do know that I love the power of the 250. I suspect that the main difference is the power and I find the 250 great in EVERY situation. :) I can take just about any hill in 4th if I can get a run at it, otherwise 2nd and 3rd are excellent. As far as I know, the 250 and 400 are essentially the same bike since 1996 so hopefully this is comparing apples to apples. The 250 is a great bike (!!!) but if you have a great deal on a 400, go for that! You can always grow into it. Best of luck and HAVE FUN with whatever you decide on!!!! *Winter Rules*