Good post with the pipe size listings. Now the trick is get a muffler that will flow as well. The straight through is the only one no matter what deadens the sound within.
David Vizard wrote a flow rate of 2.2 cfm per HP is what is needed for a nonrestrictive exhaust which will allow maximum power.
If you can find the flow rate of the muffler you want to use, in which is ether based on power or sound, OK, maybe both even, but if sound is what your after, find the flow rates of the various size offerings.
It would be advantageous to use a muffler the next size up from the pipe you have and then continue the pipe size after the muffler. This can also help keep it quieter.