@pccheese I'd start with a good benchmark program to get that information. You probably already know that there are two factors that determine the speed: the interface/controller and the device i.e. HDD. Try HWiNFO or SiSoftware Sandra. If you use HWINFO, navigate in the device tree to Bus > PCI Bus #0. Under PCI Bus #0, click on the SATA AHCI Controller device. Details about the controller will dhoe in a pane that you can then scroll through to find a heading "SATA Host Controller" with the Interface Speed Supported