Cheap and cheerful disk benchmarking
Freebie disk benchmarking: Disk Bench. Does quick tests by reading/writing/copying files of your preferred size, and tells you the speed. The only downside is it requires the Dot Net Framework. (Explains why the Disk Bench download is so small.)
I found this while pondering why my secondary computer is running so slowly. Confirmed my suspicions: Windows is installed on the slowest of the old drives in the beast. Time for a quick re-install.