Comment by ThrustVectoring

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.