I enclose screenshots of the six font sizes. The page is from HarryT's Dickens, Charles: A Tale of Two Cities (Illustrated). v2, 24 Dec 2007
. These are actual dumps of the screen, using Alt-Shift-G see Hacking the Kindle part 3: root shell and runtime system
. If the fonts look fuzzy, your web browser may be shrinking the 600x800 image - usually clicking on the image will bring up the full sized version. Note that your computer monitor may have fewer pixels per inch than the Kindle, so the image will be larger on the screen than on the actual device.
I think the line spacing should be smaller, particularly for the large fonts, but that isn't currently a user-selectable option. There is also just the one font (a bolder font, or a bold everything option, might also help readability).