@all: tx for reactions and info.

fwiw:

I have been sailing in Aruba (Carribean) we had 32knots wind, and used 41 on scale Loose & Co. (the expensive one with the two weels - sorry no conversion lbs at the moment. That number was advised by Sander Pols who we sailed with. Sanders is a fine person (he sails really well, and is very friendly). He is involved with Nacra Europe as one of the owners. As first timers on this Heineken regatta we were offered lots of help and advice.

(yes, that 32 knots was way to much for us, broke spipole twice, lots of other damage to ourselfe and gear ;-) and had the wildest ride of our lives. Never actually raised the spi. At least we had off-shore wind, or we would not have lived to tell ;-)) It was a learning experience, to put it mildly.

I guess I would start at 35 at 20knots, and work upwards in increments of 2, hoping not to reach 41 again.

>>I THINK, the best starting point is going to be to hoist the main and get the mast curve to fit the luff of the main through a combination of diamond wire tension and spreader rake. Are you running a double spreader rig with single or double diamond wires?

Yes, that is a good idea, will try that.
We are running a single spreader with single wires, like described in the Singapore threads offered by MikeMT (tx for those).

Tx for info on blogs, will start reading.