scook
Why not consider buying a standard hard drive and put it in an enclosure like this
+1 to the advice to buy your own bare drive.
That way you will know what the drive inside is. The biggest market for external drives is for backup, where speed is not critical. Some of the pre-built external drives use "green" drives or even integrate a power saving feature into the controller that slows or stops the drive periodically, and it is often difficult to find out what is in the case by reading the specs.