My understanding of part of the problem is that the basic formula folks use to determine "hull speed" of a displacement hull based on waterline length uses an approximation for the fineness ratio of the hull. That approximation is a good average for the boats the formula is usually applied to. There was an article awhile ago I think in Sailing World that expanded the fineness ratio input (actually calculating the value instead of using an approximation) to more closely represent beach cat designs, and if I remember right, the results more closely matched known capabilities.

My 18, sailed level and with the bows in (seems to go faster that way), undeniably in a displacement mode, can exceed the "hull speed" calculated by the usual off-the-cuff formula. No opinion. Newer and still faster designs may plane at the upper edges of their performance, but that seems in addition to what they can already do.