The Bisson (BCM) will be quieter due to the greater volume. Bisson also makes a strap on muffler that isn't bad. Davis Diesel offers very nice strap on German made steel mufflers that are very effective - picture attached. I managed to get one plane down to 88 Db using one of their strap on mufflers (not Pitts style). If you're really serious about noise control you can experiment with mufflers. Here are a few pix of the Dubro Arise muffler used in conjunction with a home made mousse can muffler - not a tuned pipe, it's baffled too. Very effective, and minimal power loss. Volume and baffling are the key to effective muffling. Use of a prop with more load to drop the RPM is necessary as well (less diameter - more pitch). Prop tip noise is the enemy. The slower you can run the prop (keeping the tips from approaching Mach) the better - APC props are quiter than most, those thin tips are very efficient.