The needle does play a significant part in power delivery, but it can't make a 200 feel like a 220 and visa-versa. TwoStroker is right, the 220 is very responsive to throttle position at low speeds (even with the stock pipe)- might be intimedating for a beginer. Stock, the 200 has a much smoother more linear power delivery. With either the rev or the tourque pipe, the power is still softer than stock at low speeds. With the tourque pipe the power comes on smoother and sooner, but it is controlable. The rev pipe produces an abrupt hit in the midrange and pulls hard throughout the rest of the gear. I have my racebike set up with the rev pipe, but I ride with the clutch anywhere under 1/2 throttle. You'ld probably love this setup, but your wife would hate it. I'd recomend the 200 with either the stock pipe or the tourque pipe. You and your wife would each get the most enjoyment out of this setup. (Fatty pipes are no longer available for current KDXs, though you might be able to find one somewhere, any pipe made for 95-04 bikes will fit any >95 KDX)
-Nick