Others on here have gone the 6-speed 200X route, I have not. I was going to until I saw how narrow the 6-speed gears are, and decided to stick with what I had. Also, there are 4 different 5-speed gearsets, and 2 different 6-speed gearsets between the CB/CL/SL, the XR, XL, 200X, and the utility trikes. The late model CRF230's have yet another 6-speed gearset. Some are desireable, others have some gear ratios that would be pretty bad in a 200X. I can post a chart comparing the ratios if you are interested. One more thing, to use an XR bottom end you have to split the cases and swap in the 200X kickstart shaft, it is different due to the 2 extra gears used to make it kick forward.
1985 Tri-Z 250
1985 ATC250R