However most blind people I know who do this start hating audiobooks, start hating talks, and generally by far prefer the text option. audiobooks aren't annoying, but they're below my baud if you will. Net result: boredom/falling asleep to whatever it is and the need to actively make an effort to listen. Some things which require active listener participation--math lectures for example--are different. I guess the best way I can put it is that speed is inversely proportional to the amount of, I guess let's call it active listening, required.
I've given a lot of thought to this stuff, but we don't really have the right words for me to communicate it properly. A neuroscientist or linguist might, but I'm not either of those.