Combined with my 5%-15 % example seem to suggest that it may pay off to drop the mast head spi for one that comes lower on the mast (as with cats) if that allows a sufficiently better upwind rig.

I wonder whether losing 1 mtr on the luff or so will loose 15 % downwind performance. Also going down on spi hoist height really quickle stiffs up the mast top. There is a very powerful 3rd order (power) relationship there. Going to the mast top is not a straight forward must-have.

This could be a case analogue to "slow down to win" , the well know manouvre when rounding the bottom mark with alot of other boats.

All interesting stuff

Wouter