You shouild see the Certified Pro fiber glass rods, I think there was 13 on it, and it uses every one of the once under load. So I would go with material of the blank, lenth of the blank, and its designed load points. Im sure the Rod Geru can explain this better.

John

When it comes to casting distance more guides is better as long as you are not adding to much weight. It reduces friction on the outside part of the guide were line is not meant to go. The closer the guides are together the less the line is aloud to deviate between guides keeping it running on the slick part of the ring. It also distributes the pressure more evenly on the blank. It is not quite as important on a spinning rod as the line is being pulled away from the blank not pushed into it. I believe the spinning version has 9 guides.