You can speed listen to things and use pitch correction so that it is understandable

Yes, I did that a few times with my iPod touch.

I listen at 450WPM.

I don't think I could listen that fast and understand everything I hear unless I was paying lots of attention or they are speaking about something I already know. (This is 300 words, if this transcript is accurate, and I think that if I hadn't already watched the previous seven seasons of the series I would have been like, ‘Wait... what?’)

you are still listening to every word

I hear them, all right, but they don't actually register unless I'm paying attention (or they are in my native language (Italian)).

Not if that thing uses a different part of the brain (e.g spatial/motor).

I find that I'm very bad at multitasking whenever one of the tasks involves language comprehension at faster than normal speaking rate and the other is anything non-trivial. I guess that's because I tend to think in words much more than in images.

I can read a book while worrying or thinking about something else (as always happens).

Me too, but if I'm reading too fast and on a topic I'm not already familiar with, when I get distracted I often find that the last couple paragraphs I read didn't actually register and I have to read them again. Again, that's probably because I usually tend to think in words.

Yeah, I don't spend a tonne of time in noisy environments, but your mileage may vary.

Me neither, but I mentioned it because one of the advantages I've heard about audiobooks is that you can listen to them while commuting.