The KDX has a little bit more down low, get me over the big log power, and it is better for the trails where your bars are touching trees on both sides. The KDX seems like you can let it idel down and almost stall and get back on the gas and it just goes, where the KX250F usually stalls out in that sort of situation. In the mid range, like on a hill climb the 250F is the ticket, and it dosent have as much wheel spin as the KDX, not that the KDX spins that much. The 250F also has a really smooth power delivery, and dosent really hit at all, which I like for woods ridding and racing. On the top end Im not really sure what bike is better, Im pretty sure the the 250F is faster, but the KDX does have a 6th gear, and i dont think I have ever gotten in it on a flat out run. Like I said the GNCC's where the tracks are more of a 3 hr moto cross I am racing the KX250F, and most fo the local races I well be on the KDX, my local races are 3 hr real tight single track type of races.