I would go with the thinnest, for weight concerns. When you crash, the weight will break off the exhaust flange of the motor. If you like crashing, that is. http://www.spadtothebone.net/SPAD/Mufflers/ This is the way I would do the muffler. The hole in the front makes the wavelength longer like a real pipe, but in a smaller package. If using a header, your way looks good. More adjustable for sure.