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.
In my audible library, the shortest is the first Hitchhiker's Guide to the Galaxy a 5h51m. The longest is The Power Broker at 66h9m. Most of the books I have are in the 15-25 hour range, but I also have a lot of fantasy stuff that gets near 50 hours (Game of Thrones, Brandon Sanderson...).