I used to race a bone stock 1996KDX 200 in the AMA D-7 hare scrambles series. When we ran Budds Creek, I jumped every jump on the MX track (including a 55ft table top, a 50 ft down hill double, a 45ft uphill double..) except for the 75ft uphill double called "big gulp" (where Doug Henery broke both arms a while back at the pro-national). So it can be done. It helped that the year before I was racing moto on the same track on a KX250. I would not want to learn how to jump big stuff on a kdx. It is not very forgiving. The frame and fork flex too much, the wheelbase is too short to be very stable, the suspesion is too soft, the bike is too heavy, the motor is down on power even compared to a 125cc MX bike etc. So if you want to play freestyle or MX a lot look for a mx bike, if you are just jumping little stuff <40ft, the kdx is fine.
good luck