I am looking into build a carbon wheel, and learned last night that if you are getting a clincher other than the zipps with co-molded alloy carbon rims, if it is a pure carbon fiber rim, it will have a relatively low max psi. The tire bead creates too much pressure on the carbon fiber at high pressures. read here:
http://www.rouesartisanales.com/article-20839536.html
Maybe people already knew that, but just sharing cause it was new to me. Tubulars are fine though