There's no performance benefit to using a CF seatpost. I can't say for sure about comfort, but I expect you'll do better with the right saddle than with a CF seatpost.
One thing to keep in mind is that aerodynamics will slow you down more than weight. As far as I can tell, a Topeak DynaBag is probably the best compromise between storage capacity and aerodynamic profile.
Other things you can do to increase comfort include using Fizik bar-gel, and getting a CF fork.