[tppiotrowski]

It's important to distinguish books you need to understand/remember versus casual reading. If you need to retain and understand then please take notes, re-read, explain the book to someone (Feynam method), etc.

If you're just reading casually, the content you retain from a book will be proportional to your interest not the speed with which you read it. Some parts of the book you will forget and others you will remember for the rest of your life even if you only read it quickly once.