9-10 is not a peak efficiency. Bow efficiency always increases with arrow weight (that is why heavier is quieter, there is more energy transferred to the arrow and less energy lost in the limb vibration), but at some point there are diminishing returns. In my mind 9-10 is the lower range for hunting and works okay for best vertical accuracy. For some that is the preference, but if you are shooting 10-20 yards and in, I don't see it as the optimum choice.
Shawn is right with the FOC, but assuming FOC and spine being equal, the heavier will make a more penetrating and quieter kill shot.
Either setup will kill, so shoot what feels best to you. If these are your only two arrow choices, try bare shafting or paper shooting to see which one flies best.
A straight arrow will out-penetrate a sideways arrow regardless of all the other variables.
Lastly there is the mystique and beauty of the cedar to consider. It is quite possible that may trancend science.