I have one of those Flyer 2s from Ashby which have the tilted in c/boards. One day got lazy and didn't bring the boards up and found going wild I could push a lot harder up to about 15 knots of breeze. The lift was good enough to help to keep the bows up and allow you to sit a bit further forward. Which meant the stern didn't dig in as much and in chop less rear beam slap. Above 15 knots you would want to bring the boards up as you wanted the sideways slip as the lift generated wasn't enough. But 8 to 15 I always keep down. At the Florida worlds only brought the boards when sailing flat and felt I had really good pace downwind.

This is my experience, and normally sail myself and use a velocitek to guage performance. The averages were better doing what I described for how I sail the boat.