I just installed a QA1 carbon fiber driveshaft, primarily, because of the length of my current one. At 3.5" diameter and over 59" long, I am at half the weight now with a 3.2" driveshaft. While the carbon fiber will give you less rotating mass over the steel, you won't save a whole lot weight over the aluminum.
The carbon fiber will be stronger than aluminum, and steel, and the way they are wrapping them (in house) they can make them twist like you can't do with steel, which is less shock on your tires/grip and can give you better 60-foot times. QA1 told me about one of their projects where a guy was going to steel for strength over aluminum, but then went to carbon fiber and picked up .2 on his ET... so it's possible to get better ETs, but HP is a small number.
Can they provide more HP? That's difficult to say, there's less rotating mass, but you're likely not going to see an increase you can feel... it can be up to 1% at your HP, but some of the difference could also take into effect that the oil temp, engine temp, air temp, etc., are different.