Here's my thoughts and opinion... 2.25" will be fine. I don't believe the next size up ( 2.5") will change the sound any. I ran mine all the way to the rear and only used resonators ( Hush Powers) The look like small mufflers on the outside and the sound is perfect, no resonance or hum. My only other thought is that you need to add in a "H" pipe ( X is a little better) the "H" / "X" really adds to the overall tone and helps squelch the "bad' harmonics. I added mine right between the trans bell and the basepan, it added a lot to the overall sound for the better.