I own the Spartacos, Lynn, and Sissy LeBeaux sets.  My experience with them is:

 

Sissy: Renders amazingly fast for transmapped hair (I use it a lot).

Lynn: The dreads are fast and the fro is fairly slow.

Spartacos: Fifteen jillion years with any sort of decent settings.

 

The old Karmir hair is efficient as well, but it's a much simpler mesh than some of their recent ones.

So where on this continuum are Sonia and Kouros, for instance?  I'd love to know in order to help with purchasing decisions.  I can never get enough long hair, and I love SAV's morph support, but Spartacos render times are prohibitive for use in my promos.