As i suspected thanksCertainly no point in paying a premium for a 6Gbps interface.
It's very difficult to say whether you'd see an improvement or not. 6Gbps controllers are still in their infancy and most of the ones out there just now aren't great. Even on a decent controller though the only improvement would be to the burst transfer rate which makes very little difference to real world performance. The sustained transfer rate of mechanical HDDs is still well below the capabilities of 3Gbps SATA, let alone 6Gbps.