ORIGINAL: PipeMajor
This is largely true. At the small size props we run, three or more blades will reduce efficiency. Consider the control line speed guys who run at 30,000 rpm. They will almost always use a single blade prop.
In the "sport" catagory of 11k-16K RPM's I haven't seen any difference what-so-ever!
I can imagine though that at the much higher RPM's you are talking about, the interblade wake turbulence could be a BIG issue though...
However since this is a beginners thread and we are not discussing DF or racing planes, for all intents and purposes the answer is..
No, NO difference between a 2 and 3 blade prop...