I am a big fan of variable speed playback and fast text-to-speech and I use it everywhere.
I recommend using more than one sense when you need to retain new information, for example, reading and listening. Scientists believe that there are 3 main types of learning styles: auditory, visual, and kinesthetic. When you combine these different types, you can achieve better results.
After years of experimentation, I’ve found that you shouldn’t push it too far beyond 2.6x without losing comprehension unless you have a very slow talker. Foreign accents, unfamiliar subjects, and other variables also make a difference with comprehension at high speeds. I like to move in increments of 0.2x.
For Chrome or Firefox I recommend this extension to speed thing up…
For podcasts I use Pocket Casts, check out the options below…
For Audiobooks, I use Listen Audiobook Player
For Text To Speech (Reading EPUBs aloud) I use an app called Reedy. Optionally you can invest in some good quality TTS voices in the Google Play Store and play with the playback speeds.
On my Chromebook I use this extension. It’s the best one I could find for TTS playback.