How Fast?

Yesterday on Sebago Lake in Maine, 4 of us had our DS II going at 8.2 MPH according to our GPS.... the wind was perfect! We'd never had it on a plane with 4 in it before.
What is the hull speed of the DS II... or more specifically, at what speed with the boat typically begin to plane?
What is the hull speed of the DS II... or more specifically, at what speed with the boat typically begin to plane?