On my Capricorn, I always adjust the diamond tension (= pre bend) according to the wind situation between 36 and 40 on the loose gauge. This makes a noticeable difference and I can't imagine, that there is a standard setting for all conditions. When you have hoisted the spi you have to open the mast rotation fully, so the mast can bend sideways. Support the mast by keeping the traveller in the middle (unless there is really low wind, then about 30cm open) and the mainsheet fairly tight, strong winds very tight. When you look up to the mast top, it never should bend towards the bow.
Following this you should not risk your mast, and don't ask me how I know.
My 2 cents ...
Kai