I may be wrong, but I have heard that gigantex used to make rims for reynolds. gigantex did use to make rims for FFWD and planetX, but that might have changed now. gigantex were one of the first companies to make CF rims, and they are a very very big company with regards to carbon manufacturing. they don't only make bike parts, but alot of other stuff too, so I'd say thay have quite abit of expertise in this area.
there's a article on gigantex adn a visti to their factory here: http://www.bikebiz.com/news/read/gigant ... ogy/014647
Whats different between gigantex and other chinese companies? well it's all in the skill of designing a carbon layup and choosing the epoxies you use. anyone can 'layup' a carbon rim, it takes skilll and know how to lay it up in the correct orientation to perform well. companies are never going to tell you the exact layup orientation or epoxy they use, that's their 'secret sauce'.
Gigantex is a high quality company. I would not hesitate to ride their products.