Jim Cockfield wrote:
You might (and I stress "might") see a very slight improvement for some reads due to faster access to the hard drive's cache memory (many newer drives have around 64MB of RAM onboard for cache purposes anymore)
It doesn't hurt to use a SATA III port (even with a drive that only has a SATA II interface), or it won't hurt to use a SATA II port with a drive that has a SATA III interface (as they're backwards compatible)
It also can depend to the chipset controller and drivers used.
Within my mobo (Asus), Intel chipset Z77 is used for SATA II and SATA III ports,
as well an ASMedia controller is used for SATA III ports.
But e.g. a SATA III Western Digital black drive hooked on an Intel SATA II port (300) is just a tiny bit more fast(measured by CrysttalDiskMark), than the same drive hooked to the ASMedia SATA III port (600).