No simple answer. First off, you said you "expect" that the RPMs would be 11,000 with a 2-blade. If you haven't actually measured it, its just a number out of context and is fairly meaningless as a comparison the 3-bladed prop you are measuring. 3-bladed props are inherently less efficient that an equivalent 2-blade. In theory, reducing the diameter on the 3-blade prop reduces the engine load to the rough equivalent of a "similar" 2-blade prop. However, that is not necessarily true if you're comparing a 2-bladed brand x to a 3-bladed brand y.
Given a particular diameter/pitch, you can get significantly different RPM readings from different brands of props. Some blade designs are efficient, others aren't. Some brands are light and will load the engine less and yield a higher RPM, other brands are heavier and won't. And RPM does not necessarily equate to in-air performance. If you test a whole range of props, a particular plane design will perform best with a particular brand, diameter, and pitch (at least to the pilot's senses) and its not necessarily the one with the highest max RPMs.