Looks like that may have a 12v cut-in of around 100rpm like my big servo I just got. From my limited experience, I would probably try a 7' diameter prop with that particular servo with those straight profile blades myself-- and then cut them down little by little if need be. Looking at the rated amps, maybe a 6.5' diam?? You just have to experiment. Thats one of the problems, not going TOO short of blades and sacrificing power in lower winds!
It seems that rounding the blade tip corners (about 3/4") reduces the wirling noise better.
