RE: Carbons not recommended for my bow?
I have been mentioning the AMO Minimum Arrow Weight Chart off and on for several years, but it seems to fall on deaf ears most of the time. It's pretty common knowledge that longer draw lengths produce higher speeds, all things being equal. The reason is more stored energy. Reduce the draw length and there is less stored energy, thus less stress on the bow. Therefore a lighter arow can be shot and achieve greater speed. Less arrow weight, meaning something less than the touted 5gr/lb rule if you so desire.
That being said, even with a 26-5 to 27" draw I still adhere to 5gr/lb. The only reason being that I err on the side of safety and always like to have a quiet hunting rig, which a heavier arrow provides. For 3D, where speed can be an issue, I shoot what shoots the best regardless of the weight or noise. Rubber targets could care less.
Also, as Paul mentioned, there are carbon arrows made today that weigh 5.5 GPI upwards of 12GPI for a given spine. You can actually get a finsihed arrow that weighs more than many aluminum arrows. You just have to do some homework. Visit each arrow maker's website and see what they offer because, frankly, most shops don't carry but a small percentage of the brands and models of arrows made. They stock what sells the most.