The greatest value I gain from books is in identifying how the subject discussed can apply to my own circumstances. That insight often comes to me in the pauses between pages and paragraphs where I find myself thinking on what was just read.
I might be able to absorb a bit more information from speed-reading, but I don't think I could process and internalize the text nearly as well. Since that's why I'm reading the book in the first place, speed-reading seems of little benefit to me.