I think Saito's are louder than OS right out of the box. I'm strictly a Saito man too. My experience is that the really small four stroke, like .45 and under, are terribly quiet. Especially if you put-put around. Be careful with the twins. Some come with straight pipes!

I don't own any gassers, but a local club has quite a bit of gas action. I can say that the loudest and the quietest IC model airplane I have ever heard were gassers. The "pros" set-ups are so quiet its eerie. Of course, some buffoons run open exhaust and run props with mach tip speeds. Good way to lose a field if you ask me.

To find the really quiet mufflers, you're going to have to do some searching. If you like to tinker, this could be a major opportunity for experimentation. This forum has lots of info if you do a keyword search.

Good luck.