RB Mods
Got my '99 220 carb and head modded by Ron at RB Designs and the results are really quite amazing. My bike was pretty snappy with just a Gnarly Desert pipe, ventilated airbox and optimized jetting-- but with the carb and head work, now it's got a power band fatter than Star Jones...
Really, from snail speeds to a screamin' (for a KDX) top end, throttle response is tremendous and I'm getting no trace of detonation while running 93 octane pump gas. Of course I SPECIFIED I'd be running pump gas.
If you have a 220, I believe at least getting the carb done is a must do,as you lose nothing and gain plenty. The head work is just icing on the cake; it should give you a little more snap from the increased compression AND a reduced tendency to ping due to the reshaping of the chamber. Worked for me.
Can't say if you'll get such a profound metamorphasis with a 200, though, but from reading posts on the subject, it seems like a real good bang for the buck...