Try using KOReader instead of the built-in reader software. It's a bit faster (doesn't wait to reflow the entire book if you change fonts, margins, orientation, whatever), and also it's easier to achieve consistent rendering of books (fonts, spacing, etc.) as it supports overriding the stylesheet, and just generally handles HTML/CSS better.
Oh, and speaking of responsiveness, I found that it depends on temperature a lot. E-ink apparently has a sweet spot at room temperature, but when I use the device outdoors, in either sub 10 ˚C temperatures or over 30 ˚C the screen changes noticeably slower.
Oh, and speaking of responsiveness, I found that it depends on temperature a lot. E-ink apparently has a sweet spot at room temperature, but when I use the device outdoors, in either sub 10 ˚C temperatures or over 30 ˚C the screen changes noticeably slower.