I have been using an Easton cf seatpost for about 2 years now. I have had it on 2 bikes, both are very stiff aluminum (Cannondale CAAD3 and a Cinelli Starlight). The seatpost along with carbon forks have made long rides possible. They dampen the road shocks and I am able to stay in the saddle for longer periods of time. As a test, I swapped an aluminum post in for a month and the difference was quite noticeable. I have just switched to a steel frame and have a cf fork and seatpost, what a smooth ride that combination gives me. As you can tell, I am a believer in the power of carbon fiber and its dampening effects.
My suggestion is to find a seatpost that other people have tried and have found reliable. Then, you will have more comfort and stay on the bike for more miles.