Found some more great info comparing the properties of different reinforcement material.
Checkout the back section that compares high performance reinforcements such as s-glass, carbon and Kevlar. Here's the killer table
A few interesting things that come out of this.
Carbons strain to failure is just 1.2% ( the % its fibres can stretch before they break) which is why you often hear carbon layups referred to as quite brittle. The don't' flex much but when they do they break catastrophically.
From this table it looks like S-glass has some real benefits for strength and flex over the rest except where weight is really critical. While carbon is strong and light its also very stiff so so it seems that carbon might best be used to stiffen sections of a board rather than make a board completely out of it.
Interesting that Kevlar compressive strength and modulus a so low. Other info in the above link explains this. it seems that Kevlars mode of compressive failure is different to the other reinforcements that are typically fai'l catastrophically ( all of a sudden crack and rip apart) Kevlar fails via fibre elongation ( distort and bend) rather than catastrophically and so when it fails the laminate and structure stay intact and so keep water out. This is handy for boats I guess but if you've got a bent board then you might as well have a cracked board because the bin does care how its stuffed up.