jt85,
as far as information goes, there aren't many more knowledgeable than Chad.
In my experience, I don't know if there is a definitely increase in performance, but I know that a skinny string definitely changes the spine of my arrow to where I will have to drop point weight,etc. Though I have heard it has something to do with the the string cycle, etc.
Just thinking out loud, but wouldn't a lighter string with the same weight bow move faster than a heavier string?
I'm just thinking in reference to arrow weight and speed. A 8gpp arrow will be faster than a 10gpp arrow every time, right?