You would be very impressed with the improvements made on models 89-94 and even more on models 95-01 compared to your 83 model. The newer KDX'es make the same good usuable torque down low, and with the right mods will run with a XR400 on top, but you will have the benefit of better handling.
I am riding my 2nd KDX, and I guarantee you that for the type of terrain that you described, it is one of the best options for a average rider.
I will also check out the new GG 200 if you are looking at a new bike, I have heard many good stories.
If you are not sure though, get a KDX, pref 95 model or newer, you will not regret it.
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