I had a Fatcat on a previous bike:
http://www.pbase.com/jmorton10/image/34274206/originalThat bike was a high compression(over 10.5-1), 95" motor with TW-6HG Woods cams that made over 100/100 TQ/HP. A motor setup like that makes any pipe quite a bit louder, the high compression & early intake close make for a sharp bark to the exhaust note.
I have never heard a FC on a stock motor(like a Thunderheader they are the kind of setup that is usually associated with high performance), but on my setup the FC was
VERY loud & that was with the standard baffle(the performance baffle is considerably louder).
I now ride a bagger with a similar motor & went with a Supertrapp Supermeg 2-1 exhaust which sounds & performs beautifully. I can hear the stereo just fine at any speed & while it is pretty throaty on acceleration it is very quiet at cruising speeds(the FC was almost unbearably loud during all day cruising)
~John