It might help if you remembered a lot of it in a single pass, because you aren't going to have time to go back again with such tomes. With class notes, you will be able to go through them a few times before the exam. It's usually better to learn a handful of high yield things cold than to vaguely know a little bit about a lot of things. There thus has been an intentional move by schools away from teaching right out of Guyton, Robbins, etc. Profs will still encourage you to read them, but generally as secondary, not primary resources.
I was part of the "Robbins Review project" at school last year where the class divided up the pages of Robbins and wrote practice questions to be posted on their website. I couldn't even make it through my few pages let alone the entire book. Personally, reading Robbins was not for me. I got much more out of reading BRS a few times through rather than struggling with Robbins.