That 200KTM responds really well to aftermarket "fatty" type chambers and low restriction silencers. However, it will move the torque curve up a bit and the straight through silencers are loud.
However, if it is top end power you want, that is the first step. Some of the KTM mufflers are nice and quiet, without killing power too much. I prefer quiet. But remember that a restrictive muffler and a "fatty" pipe don't complement each other well.
If it is torque you are looking for, it is impossible to get much more torque out of a small two stroke engine without resorting to major surgery. Things like big bore pistons, higher compression, port timing changes and the like are necessary to get more torque.
I hope this answers your question.
Chris