Nobody "needs" a carbon frame unless they're into professional racing or wants to smoke their riding club buddies. Assuming you fall into one of those categories, then of course you need a carbon frame.
What to get? The lightest, most aerodynamic one you can afford. Think about $4000 and up.
Below 20 pounds, 95% of your pedaling effort goes into overcoming wind resistance. It helps if you're small and skinny.
Consider aero bars.
