For what it is worth, I find that 17 knots is a very difficult wall to punch through on my Mystere 6.0. I've hit over 22 kts (in the ocean, not flat water at all!) but 17 or 17.5 is definitely the place where it gets very difficult to go much faster.
I've got recorded readings faster than 17 knots, but recordings of sustained speeds of over 17 or 18 knots are rare.
Santa Monica Bay
Mystere 6.0 "Whisk" <--- R.I.P.