Some podcasts I listen at 3x which feels near my limit of comfort (comprehension drops off at speeds higher than that), but I suspect nearly any normal person can get used to 2x speed. When you are, you can absorb twice as much information in the same amount of time.
(The above applies to talk type podcasts. Music is best at 1x, and dramatizations and such are often best left at 1x to get correct pacing).