Hoisting the spi in higher winds should be done with released main sheet and the traveller should be all they way out. If you can't sail like that downwind without pitchpoling I stop using the spi! I hoist the spi and sheet in a bit to get the boat stable and then I center the main and tighten the mainsheet, get out in trapeze and sheet the spi.
Having the main in center and sheeted hard works fine until you lose speed, then the flow over the main gets reversed and depending on which side the leach flips you will capsize either to lee or the other way!
I've tried hoisting from the trapeze but you need to fix so many things on the boat during the hoist so it is faster to get in from trapeze and do it quick and then get out again.
I use the trapeze from winds from 8 knots and higher to maintain good speed and a stable boat. In really high winds I use a chicken line and trapeze with the rear foot at the end of the hull, and once you get all the lines sorted out feel really safe and can really go for it!
Check the link below for my experiences with single handed spi sailing with the A-class.
http://webbo/~sailing/spi/index.html/hakan
