We might form fleeting thoughts much faster than we can express them, but if we want to formulate thoughts clearly enough to express them to other people, I think we're close to the ~150 words per minute we can actually speak.
I recently listened to a Linguistics podcast (lingthusiasm, though I don't recall which episode) where they talked about the efficiency of different languages, and that in the end they all end up roughly the same, because it's really the thought processes that limit the amount of information you communicate, not the language production.