I think that your lexile score represents the place where you would have 75% comprehension, which is appropriate for learning situations. But there are many cases where 95% comprehension is what you want, in which case a lower reading level would be necessary.
DS's K teacher told me, when DS was already reading at around 5th grade level, that most great children's lit is written between 4th and 6th grade level. She wanted to make sure that DS didn't think that those books were below him. Reading things like Charlotte's Web are not just about the reading level but about being part of our culture and they are great books.
