From Emory Harry :

"All other things being equal, a blank constructed of lower modulus graphite will be tougher because there is more area under the modulus of elasticity curve. It will also be less fragile for the same power because more of the lower modulus of elasticity material will be required to get the same power in the blank and therefore the blank walls will be thicker. Conversely, as the modulus of elasticity of a composite gets higher less material can be used to get a given amount of stiffness or power. This results in thinner walls and therefore lower weight. However, the lower toughness and thinner walls also means that the blank will be more fragile. It should be noted that how fragile a blank is will be greatly influenced by the design of the blank. For example, a high modulus of elasticity material could be used but the diameter of the blank reduced resulting in more layers of material used to get the desired power resulting in somewhat more weight but a blank that is just as durable as a blank constructed of lower modulus of elasticity material that is larger in diameter but thinner walled. (If two blanks have the same wall thickness the one with the larger diameter will be stiffer or have the most power). However, because the outer most layers of material are under the most stress and resulting strain when a blank is flexed, this approach has limits. As the blank walls get thicker and thicker the point is rapidly reached where the inner layers are doing very little but adding weight."
So technically, lower modulus has some advantage but a lot depends on design. If you break a rod, it's probably your fault, not the rods.

Article is below:

http://www.rodbuildingtutorials.com/...ry%20Harry.pdf

Bob