I found the storage temperature information in the http://www.intel.com/content/dam/doc/product-brief/82574l-82574it-gbe-controller-brief.pdf Product Brief.
Storage Temperature: -40˚ C to 125˚ C
As far as I know, the published specifications are not hard limits, but when you go beyond the specs, then you are in unknown territory as to what might happen. I have an inquiry out to someone who might be able to give a more definitive answer. I will let you know what I find out.