The 90 degrees is a good starting place to begin and stear from there to get as much hull speed as possible. Fast down wind is doing what you need to do to maintain hull speed. Moving your weight around is critical (This may include trapping but does not require it) In winds less than 20-22 I have found by maintaining a slight forward apparent wind we are as fast and as deep as any of the F18s and I 20s that we typically race. If your hull flys without any forward acceleration you need to do something to use that power. Up to that 20+ wind we have found it is more important to move back than out. After 20 you can start trapping or depower depending on your comfort and crew skill/dexterity. (Make sure you only move back when absolutely required. Dragging the stern is slow in all points of sail.)

Always sail your own wind. Remeber, what looks like a hot angle form your view may in reality be low and slow from the point of view on board the other boat.