All the one's mentioned above have Raid support. Ubuntu, Centos, Debian etc do it through mdadm usually. FreeNas also has raid functionality built in (and do-able graphically through a web interface I might add!).
The linux ones as well can also do your torrents & news feeds. I personally have a tiny ARM computer running Debian and it uses a combination of sickbeard, sabnzbd+, transmission to handle all my automatic downloading needs at night. You may find between the different distros it varies in complexity to install the services you require. I know ubuntu & debian have them (sabnzbd & transmission) available in the repository. I am not so sure about the redhat (and its derivitives such as centos), perhaps one of the others can shed light on this?
I think FreeNas 7 has a torrent plugin from memory.