Please attach the HWiNFO Debug File which should provide me with additional details about this issue.
Alternatively, you might check in the PCI bus tree - locate your SATA controller device and check particular SATA port status.
This is because the storage driver doesn't report actual transfer rate, while the Seagate drive itself reports it. The WDC drive however doesn't.
So I'm afraid there's nothing more I can do. You should rely on the PCI-SATA controller information.