I have an 04' fxsti with cycle shack slip ons, sounds really good, its notloud at cruzingRPM but drop one and giver sum and your buddys will hear ya comin.
I had cycle shack slip ons on my Fatboy and they sounded real good. I originally planned on a full exhaust replacement but after hearing those I said why bother.
I have the V&H slip ons. Got them from Rons cycle shack on ebay for around $200. They went on real easy and sound great. Not to loud but they will hear ya comin. Performance was good and no re jet needed.