You'll be going backwards if you choose to go with a spark arrestor silencer,they make DBs a little lower...I've never used a "Sparky"(I know what they are),but I'm thinkin it will also cut down on DBs.
The four strokes are just obnoxiously loud....you're only gonna be louder than one if you run no silencer....and unless you're strictly drag racing,I would'nt reccomend it.