When I was taking the course, they said that two things slowed one down when reading. The first was the eyes’ tendency to flick back and forth over words already read. By forcing the eye to follow the pacing hand, that factor is eliminated. The second thing that slows one down is the ‘need’ to say the word to oneself as it is read. If you can break that habit, you are limited by how many words are on a page, since more time is spent turning the page than actually reading it. The best in our class was at 10,000 words per minute at something like 95% comprehension.
I know I was able to reread a whole quarter’s of assigned texts (four or five books) a half hour before the final.
I’ve always struggled with “saying” the words in my head (it’s call subvocalization). I see the word and I automatically “speak” it.