Not sure this post is in the right area, but here is my answer to your question anyway! I have a 2004 FLHT (E Glide Standard) with Fuel Inj. I have a Ness Big Sucker breather, Power Commander IIIr (not usb
) and Sampson Rolled Thunder slip ons. I am running stock pipes from the engine to the slip ons, so I have that poorly designed cross over for the rear cylinder......someday!! With all that being said, I have NICE deep rumble, not super loud (unless coming/going from military family housing in the wee hours of the nite or really hitting the throttle). Performance pick up was good.......Not great (think it could be tuned on a dyno for more performance), but I am happy. I get the sound that I wanted, nice deep rumble without being totally obnoxious in the volume department. I have enuf loud to turn ALL the Germans heads (except those that are deaf!) as they have strict sound/muffler laws that they must comply with. Your best bet is to go to some biker events, listen to different bikes, if you like something, ask them what they have. That is what I did and have been very happy.
Good luck!
Especially while playing a bit of free way tag. 
