Forget the Cato three blade, just put a 6 or 7 inch Saber extension on the crank. Takes a lot of engine noise away immediately.
I'm running a O290D on my Varieze with a new Hertzler prop and 6 inch Saber, I couldn't believe the noise level difference. And I agree a muffler is a no o for performance, If you want quiet by a electric powered aircraft or a Bose headset, Lightspeed are great too.