I went the opposite way, from a 99 kx 250 to 2000 kdx 200. The KX was a bear in the tight stuff even with a 9 oz flywheel weight. The stock suspension on the kx was non-complient in the nasties also. It sounds like your kx has all of the necessary modifications to be a good wood weapon. Good luck and post a ride comparison with your kdx.
My kdx has all of the typical modifications and is a much better in the woods than my kx. After riding my friends 03 ktm sx 250, I am considering getting another 250. I really do miss the 250 power.
kx250
kdx 200