As it was explained to me when I asked at the shop: Carbon shafts retain more energy which is transfered through flight and ultimatly impact. Thus you get a faster traveling arrow with strong impact. When I switched, I noticed a definate difference in the speed of my arrows and had to adjust my sights. Now that I've used carbons. I won't go back to aluminum.

Carbon Express terminator 6075 with Spitfire 100gr Mechanical broadheads.
I am much more accurate than with aluminum.[8D]