I've been practicing speed reading on and off for several years now, and I can say it takes practice and extra concentration to get fast. I can easily get to 650 wpm now, but only if I remember to do it... I'm still practicing and maybe one day I'll get to over 1200 wpm (my current goal).
It's not easy to keep the concentration required to understand while reading much faster than usual, but it's a good exercise for the mind.
I'll try the practice you suggested at the end, thanks for the post.