I beleive the rule is to drop one inch in dia if you add a third blade. IMHO 3 blades are neat but you don't get much for the price. I do want to use one on my Saito 450 though. I beleive the Saito 100 likes a 15x6 which would mean using a 14x6 3 blade. I would test and check with a tach. If it loads the motor enough that you are getting less than 8k I would not use it. Notice that each brand of prop will give different results. I used a APC 17x8 on my Saito 180 and it was happy, following the "rule" a 16x8 should give about 8.3k. Personally I like the pull of large dia props and use the pitch for adjusting speed within reason.

Carl