cyco1450,
I totally agree with you, the 2.25" flows better than a 2.0", and logically would make more power, but that's what I was told on the phone the day I placed my order. I don't know how much louder the 2.25" is than the 2.0", but I'm totally happy with the 2.0" Fullsacs. In 6th gear it is very mellow until 3 grand, then she starts talking. I cruise a lot at 80-85, then the slightest increase in throttle, it really sounds good.
My '05 WG has V&H BigShots w/Big City Thunder power chambers, and it is LOUD. A very good sound, and the baffles/chambers hold enough backpressure that it still has a good flat curve on the dyno, but it really barks. Most of the bark is the S&S cams and 10.5 c.r. On any given day, there are 20-25 Harleys at my work, and I've been told many times by the other riders that my WG sounds better than all of them.