When you speed read, you can grab the words off the page faster than you can understand and fully process the information conveyed by the text. How much time you have or want to spend re-reading or thinking about what you've read is quite obvious. There's a stark experiential difference between reading an informationally-dense passage and one that spends a lot of time rephrasing things, using LLMisms to restate concepts, adding in extra connecting phrases, etc.

If your reading speed is limited by how quickly you can subvocalize the words to yourself, this is significantly less obvious. Unless the passage is dense enough to require multiple read-throughs at conversational reading pace or vapid enough to be boring, you're going to feel done with the text at roughly the same time. Speed readers do a lot more re-reading and varying of reading speed, and that is going to correlate pretty hard with information density.

I haven't looked at the book since the 80s, but what I remember is there is a pre-read, the fast read, and then the deep read as needed depending on the task.

pre-read is just looking at how long it is in the headings, and planning out what chapters to focus on if it was a text book. (its sort of iterative, you do a pre-read for the whole book, and then for each section you break it into)

The fast read you try to read only with your eyes, sweeping your eyes across multiple words at the same time, suppressing the urge to say the words to yourself in your head.

iirc the how to read better and faster book even had a cardboard mask you put on the page to practice the sweeping, and some pages that were laid out weird to try to teach you how to do it.

Some ai text just seems really easy to speed read, like if it's tuned for an easy reading level. In PRs some ai seems like it's arguing over weird flex technical details and really starts torturing the language in a way that makes it the opposite of easy to read.