It has already been mentioned but usually it is preferred to have a lower profile rim for crit racing with light weight. That being said it seems like a lot of guys these days go for the semi-aero/aero wheelsets such as the carbones, 303/404's, etc. I do not know if that is because of the bling factor or that people actually do like them more. I see the practicality for larger riders who are more putting more power to the pedals (not my case at 69kilos) but otherwise I think it would be more beneficial to have the ksyerium ES. We just had the mavic rep for the shop I work for come in and talk to us about that issue.
Oh and regarding someone who said the carbones just have a carbon fairing, that is completely false. Probably not good that a shop owner told you that...may wanna question their expertise in the future. Just take a look at one of the demo wheels and you will quickly see that that is not the case. It is just a difference of the braking surface between the carbone sl and es (I think I am getting those model names correct...if not, someone please correct me!). The sl has an aluminum braking surface whereas the es is an all carbon wheel. Still, with the sl the carbon is not just a fairing...the majority of the rim is CF with an aluminum braking surface. All that being said, I want a set of Reynolds
!
~Nick