That's fairly short. I read about 100 books a year and it includes thousand page tomes like The Count of Monte Cristo.

I always assumed that book to be rather short since it just needs to be a number of sandwiches eaten.

100 books/year. That's an impressive feat regardless the number of pages. Are these downloaded ebooks or physical printed copies of books?

It's mostly audiobooks, I have some ePubs that don't have audiobooks anywhere, such as many Japanese light novel fan (or official) translations into English for example. I can get through them as I can understand audio faster than I can read text, as I play back at 3 to 5x speed.

what's your retention/comprehension of the content at those speeds? i find that those speeds allows me to understand the concept as it's whizzing by, but the retention of it is not good. everything i've ever been taught and personal experience about long term retention all say speed is not the most conducive.

Retention is pretty good but that's because I've been training myself for the past 5 to 10 years to get to that speed. It's similar to how blind people's TTS are incomprehensible to most hearing-able people.