Mildly tuned two strokes that are designed for low rpm use can and often do beat four strokes at their own game. That includes being quiet and good fuel economy. I had a Kadet Seniorita powered by a OS .40 FP. Using a 11x5 APC prop, the plane was so quiet that one of my neighbors thought I was flying an electric plane. This engine also sipped fuel and I had no problem getting 15 minute flights out of the plane's 6 ounce tank.

A lot of the noise that high performance two strokes get blamed for is actually coming from the propeller. Watch this video of this high performance electric plane to get an idea of just how much noise propellers make at high rpm's.

http://flyemfast.com/files/BestVen.wmv