I think that you should superread and dip until you feel that your purpose has been accomplished in reading the book. The point is that the mind does alot better if you do it in 20-30 minute spurts. Beware of overdipping. Only dip in if the words seem to draw you or "jump" off the page. That is your minds way of telling you that there is something there to edify your purpose.
Remember, study as much as you feel like you need to, but do it in short bursts with regular breaks.
If you have a general need to know more, but can't put a finger on it, then rapid reading is in order. I have photoread about 10 books in the 2 weeks since I finished the course, and I have to feel the need to rapid read.
