hi.
people say, that u must take one from pitch from 2 bladed prop. n your case u need 16X6.
thay say, that when going to 3blade props, u loose thrust. someone says that u loose speed too.
in my case, (i have mag91fs) i used 13X8K MA prop and had thrust 3.6kg.
than tryed 13X8 MA 3bladed and had 3.8kg thrust and about same speed.(maby more). but engine abviously was spinning slower. it had less max rpm. but didn't overheated.
I think that on 3 blade prop u must maintain low rpm. it looses effeciency at high rpm-s. so i'll think, that if your engine spins 17X6 fast enough, if i were u I should try 17X6 3 bladed. thats just my opinion