The Cybook may be a better choice than the Kindle for a 6" device. The Kindle has one font and 6 font sizes, see
Font Sizes. The Cybook has more sizes, and a larger maximum size, and you can change the font - see
Does the new CyBook support ultra-large fonts. The same thread (post #13) includes a screenshot of the iLiad, which shows a larger font still. With the iLiad you also have the option of FBReader, which has even larger font options and better hypenation (good for large fonts on a small screen), see also
Things you can do with your iLiad. Note that screenshots will likely appear larger on a PC screen, because most don't have 160-167 ppi like the EInk devices. Printing on paper at the actual screen size is the best guide.
I think the iLiad Book Edition maybe your best option but it is expensive, and the Cybook may be "good enough". You can buy the Cybook from Books on Board in the US.
I really like my iLiad for reading around the house. It is possible to use it when traveling, but the 6" devices are more convenient because of size and also battery life. The iLiad's page turn is slower than other devices, but its screen is larger so this probably comes out even.