I don't think that there is a serious difference between the cables and either way, no hard drive that you'd have is fast enough to make use of SATA3 anyway. Supporting something and being able to make use of it are two different things. Fr example, a Radeon 7750 supports PCIe 3.0, but a PCIe 2.0 x4 slot would hardly impact performance on that card compared to a PCIe 3.0 x16 slot that has about eight times higher PCIe bandwidth. Hard drives simply tend to not saturate SATA 2 except maybe for their cache, but even then, it doesn't make much of a difference. SATA3 support on hard drives is kinda gimmicky as far as I know.