I find broadcast speech in general, and especially recorded narration such as audiobooks, to be slow enough as to provoke distraction.

On top of the additional focal intensity, there's double the time bandwidth. Of course, it's sensitive to my mental state -- sometimes when I'm de-energized I need to slow it down to 1.5x, but I'd ideally hover around 2.5x (though software rarely goes above 2x yet).

To get started, listen to something at 1.25x, and crank it up further as you get accustomed to the density.