Dual hard drive setup in early 2011 MacBook Pro 17" (replacing optical drive with HDD)
UPDATE: I purchased a dual hard drive adapter for swapping with the optical bay, and installed it in my machine with the original 500GB SATA III that Apple shipped with the laptop. So far everything is working just fine, and I have two working hard drives in the machine (triple booting Lion, Yosemite, and Windows 7 via Boot Camp). The second HDD is displaying 6.0 Gb/s link speed, with a 3.0 Gb/s negotiated link speed. I understand that even though the HDD is SATA III, it's dropping down to SATA II speed; but so far there aren't any problems with the disk running, and I can boot Lion from it without any issues. Will post any further developments.