Ray,

My guess is that this question would be difficult to answer for even a plastics expert. You might get an answer for a test sample subjected to what is called an Izod test for either knotched or unnotched samples. But this would mean little in the real world. Things like resin type, surface treatment, scratches, section, reinforcing material (graphite or glass), age, temperature, scrim type and angle, load application, and much more would influence the outcome in an acural rod. But I bet, in the real world, whatever breaks a glass reinforced rod would most likely break a similar rod with graphite reinforcement with all other items being equal. I would be careful with both and if I broke it, I would blame it on me rather than the reinforcement type.

Bob