The amount of twist and how much sheet to let out is definitely a judgement call. It depends on wind speed, etc.
I was reading something about twist last winter in Bethwaite's book " High Performance Sailing." Then I checked some pictures of the guys that were pulling away from me downwind. They had twist whereas I was sheeted tight. Tested it last summer and the twist allowed me to stay with them or maintain a lead.
Tom
IIRC Bethwaite (I have the book too) talks about matching leach curves/exhausts between Spi (least control) and jib (more control) and mainsail (most control), which I agree with, but I feel we have to balance this against the need to support the mast too. This is why I advocate some downhaul when sailing down wind when it is windy, it opens the leach of the main, but still supports the kite as the bend in the mast is aft - this does then load the mast more in compression (but I've never been worried about this with the 17 mast as it is large in section / mass) - I am muchmore worried about the kite pulling the top forward and breaking in this direction.
