As I was reading this article, I used the SpeakIt! Chrome Extension[1] with the native voice setting to gauge how fast the quoted speeds actually are.
For me, 800 wpm was about the limit of how fast I could read while still understanding most of it. That's the '4x' setting. The '2x' setting is 400 wpm, which based on the article and my experience is a good target reading speed.
It's not entirely perfect because the rhythm imposed by the text-to-speech engine is not optimal for fast reading – it pauses when you don't need a pause and powers through complex sections, but I found it an interesting exercise nonetheless.
Lately I do most of my reading by listening to audiobooks. The last two books I read, I experimented with the 2x speed setting on the iPhone. It took a few minutes to get used to, but now I can't recommend it highly enough. Now I can get through audiobooks in half the time and I've totally adjusted to the butchered sound quality.
[1]: https://chrome.google.com/webstore/detail/speakit/pgeolalili...