I'm going to take a stab at answering Vic's question:
5. is there any advantage to being set at 40 mm which seems to be the max set back over 25 mm which seems to be the min set back?
First, while the position of the mast step, rake, and pre-bend are all tied together, they are also separate
Position of the mast step, by itself, should not affect the mast rake. In other words and for a moment think that you are starting with a mast that is straight and verticle (perpendicular to the waterline), then, moving the mast step aft, will not necessarily move the mast tip forward. Moving the mast step aft with the mast fixed at the deck will cause the mast tip to move forward but if the mast is free to move at the deck, then moving the step aft will move the whole rig aft thus moving center of effort aft which, in theory will induce wheather helm, which should help light air performance.
However, moving the step back will, in effect, reduce the amount of rake that can be induced (with the mast step further aft, the entire mast is moved back closer to the back of the hole at the deck level) therefore the mast will not angle aft as far as it would if the step were further forward.
Although I have not trigged this out, my guess is that moving the step back from 25mm to 40 mm will not induce as much affect on moving center of effort as setting the step at 25mm and raking the mast.
After mast step position is set, shroud tension, forestay length and backstay tension, as adjsuted, will then determine rake and mast pre-bend. Depending on where you want to induce mast prebend will affect when you block the mast at the partners.
