It was me that said that many pro's don't change their downhaul setting. The was a person who said that you would need many sails then.
I use 9.8 from 4-7m/s. 8 from 7-10 and 5.8 until about 15 m/s and i very rarely adjust my downhaul. So i can sail from 4-15 m/s with 2 boards and 3 sails only adjusting my outhaul.
I don't understand the "rig as small as you can" thing. Not unless you jump and do tricks. Better to be well powered up with good control and the power low in the sail.