If you have flat'ish water and
LOT's of wind (eg35-40+ knots), the issue I can become more about control rather than power and efficiency. If you don't have a cammed sail small enough, you will probably do better on whatever you have that you can still keep completely under control and be able to apply the power you have.
Even in moderate winds, a well balanced setup with a good no cam free ride sail can be only a knot to two behind a cambered race sail.
No one aspect of your speed setup is as important as the total balanced package. The board, fin, setup positions of straps and track and the setup and type of sail all must work together to complement each other and your own size, weight and skill level in the particular conditions you have. If any of these things is way off, or the components are not well matched it will drastically affect your ultimate performance. There is no magic formula for this but logic, trial and error and experience will help you find the balance.
eg: Back in about 2006, I went out on my SB Acid 74 wave board with standard wave fin and 3.7m KA Kaos wave sail in a 35+ knots Easterly at Sandy Point and cracked 40 knots peak speed. What is normally a relatively slowish board turned into a rocketship in 35+ knot gusts on flat water as it got up on the last few cm of the narrow pintail and took off downwind. I am sure I would go at least low to mid 40's on my CA40, 18cm Tribal speed fin and 5m KA Koncept in the same conditions now, and do it much more consistently, but hell it was fun!
