Speed reading might not help too much on LSAT reading. Speed reading can help you go through a novel, but the same notion doesn't hold true for LSAT reading. If you storm through a novel, what you omit is probably doesn't hurt understanding the story. LSAT reading is so condensed and if you miss a few sentenses, you might still be able to understand the passage but you might not asnwer all the questions right. I tend to agree focus on the questions. E.g. for certain type of passages, what questions are "FAQ"s.
Also, I need some tips of how to "selectively" read the passage. Of course extensive reading always helps.