There are currently no mechanical hard drives that can benefit from the use of an SATA III controller port, even if the hard drive has an SATA III interface. They simply don't pump data quickly enough.
I'm using a velociraptor myself, as Plumble suggests. In theory, a highly cached drive like the Seagate Momentus might give you an advantage and, rarely, benefit from the SATA III interface.
(I'm assuming from the 6gb/s in the thread title that you are inquiring about SATA III.)