Brad, I had the same question shortly before I bought those headers. Check out the thread below. Theres another link in there to a thread about a Patrick Motorsports sport muffler.
http://forums.pelicanparts.com/showthread.php?threadid=146714&highlight=megaphones
Consensus was that the megaphones would only result pissing the neighbors off, losing midrange torque, and violating every noise ordinance in existence. My plan was to use the RSR headers to street adapters to a sport muffler from Patrick Motorsports.