Maybe you guys can help me get it straight. On a 2 stroke it seems like you change the header part of pipe with an after market header for performance gains whil the silencer isn't as important....but on a 4 stroke you change the silencer for max gains while the header isn't as important. Is this true? Also is the pro circuit exhaust the way to go on the 06 KXF? I tend to trust Mitch but who knows.