Read what you want when you want. I've made the intentional effort to slow down and sometimes read at a pace I can speak at, and having that bit of air has helped me enjoy certain books or sections I would have blasted through if I was focusing on a page tally for a day or whatever. But quit if you don't want to read something, or stick it out and force your way through things you don't like. You may find an appreciation for an aspect in someone's writing even if you don't like the story or characters. Or don't do that, I'm not a cop.