If it's any kind narrative (biography or fiction or whatever), I generally whiz along at ~200-225 pages per two hours as I gradually cease reading, and my imagination takes over... eventually, it's like I'm watching a movie, and it only stops when I reach the last page. If it's nonfiction, it really varies. It took me months to read The Rise and Fall of the Third Reich, due to the heavy subject matter and the enormous amount of information. If it's a textbook or academic paper, it may take me several minutes per paragraph, due to the necessity of grasping the concept before moving on. In terms of persisting, I found it worthwhile to keep trying to read The Rise and Fall of the Third Reich, even though I probably missed out on reading easier fiction.