I've been playing around a bit with Savitsky's planing hull formulas, and have gotten results that seem to match my own experience.
For example, the graph below plots the supported weight for a flat 1400mmx400mm plate at 4 deg AOA.
At around 15 knots (7.5m/s), my 90kg weight is nicely powered on my 1400x450 board. Of course, many other variables need to be taken into account, but as a rough guide the formulas seem to work nicely.
Anyway, attached is the original Savitsky thesis, and my little spreadhseet.