No hard drive has platters that spin fast enough to require 6Gbit/sec SATA. The maximum transfer rate of the fastest hard drives is way under 3Gbit/sec. 6Gbit/sec SATA is only required for the fastest Solid State Drives which aren't limited by mechanical speeds.
Think of it like the speed limit on a highway - just because the speed limit is 60MPH, it doesn't mean that bicycles are going to travel at that speed.
Ah thanks for that, will definitely keep it in mind! Will have to hope to what the future brings i guess