Mike McConville used a Bolly prop on a DA-150 at our Imac contest a few years ago. Not sure of the size, but it was the loudest prop rip I've ever heard during a freestyle. Nearly everyone had their fingers in their ears, and a smile on their face. If you want to make the most noise, use a low pitch prop with a large diameter - this will get the tip speed up in the supersonic range. Bolly carbon prop or Menz-S wood.

Loud props save lives.....or something like that....