Acceptable Drive Temperatures

When I rean SpinRite on an 80GB SATA WD drive this morning, it shut down because it reached 56°C, which I believe is the upper limit. What is a good temperature for normal operation? Some of my drives are at 29°C, one is at 39°C, and the new one that I got this morning to replace the 80GB drive is at 45°C.

If you go to the WD Knowledge Base and type in the model number of the drive, you will find the Spec Answer for the drive.  In the Spec Answer, you will find the upper heat limit the drive should run at.

WD Knowlege Base