RE: Dragging bits of your bike on corners. All motorcycles have a point at which they will drag various components. The limiting factor is when tire adhesion to the road surface breaks before parts start to drag. Some bikes have crazy lean angles, like road racers, sport bikes and BMW GS's and the tires will give up at or very near the point when hard parts touch the ground.
Any exhaust system that runs along the outside of the frame is going to be prone to touching the ground at extreme lean angles. Like everything else, there are compromises involved regarding looks and performance. Loud is not necessarily going to equal fast, nor are larger diameter exhaust pipes the answer.
I usually drag the foot pegs before anything else hits and for me that is the perfect way to tell me to back off a bit.
Factory exhausts are engineered to produce torque over an RPM range that complements the motor's torque curve. Less restriction usually means better performance at wide throttle openings, but low end torque will suffer. Small diameter, higher restriction exhausts will give better low and mid range performance at the expense of wide open throttle horsepower. Sound wave propagation has a lot to do with how exhaust systems produce, or hinder, performance. Not germane to an XS, but wave propagation is the reason why two stroke exhausts look the way they do.
The trick, of course is to balance the bikes engine output with an exhaust system that complements the riding style of the operator. My XS had 1.5 inch head pipes and with the mufflers I installed it has about as perfect a torque curve as you would want for a street bike of it's displacement. While I know that tuned, equal length header systems will produce more power through whatever RPM range they were designed for, I personally prefer the classic dual pipe/muffler look.
