You may be able to get a larger font still on the iLiad using PDFs (customized to the screen size) or FBReader, and both support multiple fonts and will hyphenate which helps for large fonts. In any case, the practical limit is set by the size of the screen where the iLiad wins easily. For screenshots of the iLiad, including the contentlister (menus) see
Things you can do with your iLiad.
Also, see
Does the new CyBook support ultra-large fonts and
Font Sizes.
For actual size screenshots (bitmaps of the screen) print them on paper at 4.7" by 6.2" (iLiad) or 3.6" by 4.8" (Cybook). This is very close to what the device will show, except the background is grey rather than white.