“500 pages per day” — this is not truth, because really is 500 pages per week. See this story from Buffett`s investment manager Todd Combs: https://www.youtube.com/watch?v=SqUyRnv50pg
This may be original mistaken text http://www.omaha.com/money/investors-earn-handsome-paychecks-by-handling-buffett-s-business/article_bb1fc40f-e6f9-549d-be2f-be1ef4c0da03.html May be it’s just typo.
One more thing. 500 pages in context is 500 pages of “reports, trade publications and other papers”. And is not equal to 500 pages of a book. It’s different type of information and different manner of work with information.
Finally, important not the quantity but the quality.