Let me clearify.

Indeed "Long luff = speed and depth", but is lengthing the luff at the bottom of the spi so it moves between the hulls just as beneficial as lengthening the luff at the top.

I think you'll find a great difference here. Therefor I postulate that "Long luff = speed and depth" is not accurately enough in describing the situation and therefor possibly misleading or indeed wrong for a given seet of setups.

We need to get away from overly simple (Neatherthaler) statements of the kind "Steel and concrete = good, wood = bad"

Wouter