I doubt regular folks can reach 5x or even 2x with good retention. Perhaps if it's a podcast of people chatting about random things, it's possible, but any intellectually stimulating content you probably will have problems. Visually impaired people probably have an advantage on account of having their entire visual cortex freed up and possibly able to help with this (not sure if it does, neuroscience majors here?)
(As a sighted person) I watch all my videos or podcasts at 2x. Depending on how new or dense the content is, I might have to occasionally dial it back, but I think I do fairly well at 2x (usually, this is only the case if I'm distracted or the slides are going by too quickly as well). Often I can even up it to 3x.
