I've noticed blurry text with some font sizes more than with others. Try with various font sizes to find the one that will produce a crisp readable result.
I believe the issue is somewhat similar to using other than native resolution in your monitor. I mean, if the computer says a line should be one pixel wide but the monitor will try to draw it like 1.2 pixels wide, the image will be blurry simply because it's impossible to illuminate physical pixels partially. Just as you can't light up 1.2 lightbulbs out of 2, it's either one or both if that rough comparison makes my explanation more understandable...