Eric, I do not believe the blade thickness was the concern. The speculation was that the shape of the XMP blade may have been more sensitive to flex at higher (prop) rpm's.
Im not sure what else would explain the phenomena that we're describing here, but feel free to enlighten me! Like Kyle, he saw the last 300-400rpm add little to no speed. Where are those extra RPM's going if theyre not pushing the boat any faster?
Kyle, in theory, the fewer the blades, the more efficient the prop. Ive found the 3-blades Ive run to be a bit faster than the 4's. I think that the large blade surface area found on the modern CNC props largely levels the playing field between 3 and 4-blades, at least for applications with relatively low loads (skiing and footing). If youre show skiing or running a wakeboat with 2k lbs of ballast, I hear the 4's still do better for the big loads, especially out of the hole.