I rode a 220 with all the goodies for a couple of years, and now am on a 01 RM250. I am TOTALLY delighted with the RM compared to the KDX. It handles MUCH better, suspends better, and the power is in a whole different township compared to the KDX.
Keep in mind, the 250 motobike is not for everyone; it is NOT a beginner's machine. ie- If you want a pleasant trail bike, buy the KDX. As far as the increase of intensity, it will be a pretty big step, but the flywheel weight on the 250 motobike does an excellent job of toning the bike's hit, as well as reduces the tendency to stall.
BTW, I have ridden a bud's 01 CR250 in the woods, and the RM is without question, a much better steering machine. The CR has a more aggressive powerband, whereas the RM is a little easier to live with at lower revs. (both are PLENTY fast at upper rpm) I will admit that I am impressed with the Honda's quality of construction, but the Zuke is no cheapie either.
&btw, forget those WR/YZ250F... unless you want a bike which is difficult to start. Anyone who says they are easy starters is blowing diesel smoke.