For the slip ons, my builder suggested Krome Werks 3.5" Is anyone familiar with them? He claims they are a nice, tamer muffler which I wouldn't mind due to the touring miles I do.
I have the 4" and really like them, but for me they are a tad too quiet (but not by much). I'd like to hear them without the cat in the head pipe though. Fit and finish is great!
4" touring - quiet,more for low/ midrange . 4" performance ,little louder,midrange / top end or for a more aggressive build
3.5" touring low/ midrange Little louder than above, the 3.5 lite is probably the loudest and has the least restriction although, I have never heard this model.