the flex response and weight make the carbon boards faster.
If you want durability go for the model down (Fiberglass/wood and carbon mix depending on brand), or get an SIC, they are both more durable in my books than carbon from other brands.
Some Fiberglass mix boards are now days only 1-2kg heavier than carbon so lately I have seen a few guys go there and not actually affect their paddling too much and end up with a board not much heavier and more durable