Royce''s Illustrated Sailing has a good section on this. Somewhere else I read that a broaching wave is about 40% the length of a modern displacement hull boat.
The power of the wind against hull and sail area is a squared-function (ie double the wind velocity = 4 x the power) So serious reduction of sail area, leaving only steerage, would help alot. Also, close reaching in winds at Force 6 is next to impossible in most recreational boats. I personally think of Force 7 as heavy weather but then I''m a wuss at this. That''s 28-33 knots. Get off the water if you can, or heave-to if you can''t.