Adam, I have owned 3 kx 500's. starting with the very first, (air cooled) that came into my state. They are my second favorite 500cc two stroke, which is saying a lot. In stock form they feel too wide. My last one which was bought to build up and sell was a 2002. through it all I kept the first water cooled cr500 I ever had. The slimmer feel and the wider ratio trans that you can get for a cr500 is just a little bit more to my liking, not to mention that it makes the same hp, but at a lower rev range than my KX's did. and WE DONT NEED NO STINKING POWERVALVES.
the idea of a kx500 in the new af of its third cousins is pretty interesting, but not enough to make me part with the money, just like the af cr isnt.