Internal 1TB Sata III for Macbook Pro 2011 (for the OptiBay, as a compleent to a Vertex 3 IOPS Max). Do they exist? If yes, what brand is it and what kind is are reviews like ?
The only 1 TB drives on the market that would fit in the optibay are SATA II, which is fine, given that there is no platter drive on the market that can even saturate a SATA II interface. Make sure you get one that is 9.5mm height, not 12.5, which will not fit in the optibay.
from the above, I understand that no 1TB HDD is able to provide enough read/write speed to justify a 6Gb interface (or even3GB ?) ... My only option is to get a drive that fits the physical space... Am I right?
Not necessarily. A Velociraptor may fit, but it needs a 12V line which your laptop doesn't have. Normal 2.5" HDDs up to 9.5mm will work fine in the ODD space (and up to 12.7mm in the regular HDD spot).