I guess I may as well chime in on this one too. I had a silencer go bad, one of the internial baffles cracked and broke away. Sounded cool at idle and off idle for about 5 minutes! It didn't make any more power, shift RPM's were the same. As the day's ride went on, it got old real fast. My right ear was sore for 3 days, and it wasn't as loud as some race pipes.
The pipe builder engineer's a pipe to operate with a certain amount of back pressure. If you change that back pressure, then you"ll need to change the pipe chamber, and/or outlet to regain any lost power. Sure it may "sound" faster, but is it really?
Then there is the issue of loud pipes closing riding area's. IMO, do yourself and your riding buddies a favor. Keep it quiet, we dont need to loose anymore riding area's then we all ready have.