sjon,

read the landenberger tuning guides i posted here. should answer all hidden secrets.

just to answer your questions:

as lighter you are, so more spreader rake you need.

so lighter you are, so more diamond tension you need.

still i know really have guys who sailed quite a lot of spreader rake with very loose diamonds. i think that is a general development taking place.

more spreader rake can help you a lot to enable the top to twist much more controlled with nowadays sails. just pulling cunningham to the max without paying attention to a reasonable spreader rake is simply not comparable in what comes out of it, specially in terms of the desired autodepowering twist.