In general, the more you read, the better your read.
For me, fiction books are easy when getting into it. It's like watching a movie unfold inside the head. It's simply difficult to put a good fiction book down.
Non-fiction in general is not as fast to process. But, sometimes books have a lot of redundancy, explaining things already explained, repeating the same thing over and over, and repeating the same thing over and over, and explaining things already explained, and so on. I just skip that without remorse.
I speed read when it makes sense (for example, when finding some information fast in a mass of unknown text). I take notes in different ways, sometimes use a mindmap and use different techniques to analyze and remember.
I take some breaks, too, but they are not scheduled nor regular. The ideal break is a short walk outside, but this is often not practical.
Doing 350 pages of non-fiction in a normal weekend is hard, unless I'm alone without family, eat takeaway and have some background knowledge of the subject and can skip some parts since I already know it. For something completely new, maybe 3-4 days is more accurate an estimate.
Doing 350 pages of fiction is very fast, specially if it's in my native language. Other languages are a bit slower to process.
Last but not least, if it turns out that the author is stupid and/or the content is rubbish, then reading the book becomes hard work. Therefore, I think one has to have some form of interest in the book as well to motivate reading the book at all and to be open to consuming the book effectively. For me, this interest is actually one of the key things for consuming a book. For example, once I had to stop reading one of George Friedman's books for the aforementioned reasons; thinking "this is such bullshit" after every few pages is not a good signal.
One way to build up this interest towards a book is to create, beforehand, some questions which the book should somehow answer.
Hope this helps and gives you some ideas.