“The motor response of the retina, and the time it takes the image of a word to travel from the macula to the visual cortex for processing, limits the eye to about 500 words a minute.” Worse, most people top out at half that rate. According to Wired, May 28 at 121, there is no such thing as speed-reading if reading includes the trivial detail of comprehending the text.
If your in-box piles high with reading material, your best approach is to read selectively, deliberately build your schema for understanding what you read (See my post of April 23, 2008: mental schemas of experts are richer.), and try to absorb no more than what is necessary (See my posts of April 5, 2007: expectations that law firm lawyers will read about one’s company; and June 16, 2006: costs of reading emails.).