Here is thread wherein we can compare and/or discuss fonts on the Paperwhite and the other Kindles which have a lower resolution screen, for example the Touch and K4.
The Paperwhite has a screen resolution of 758 wide by 1024 tall whereas the other Kindle 6" eInks have a resolution of 600 wide by 800 tall. Interestingly the Paperwhite has a slightly elongated ratio than the other 6" eInks--if we scale the Paperwhite's resolution down to 600 wide we see it is equivalent to 600 wide by 811 tall, which is slightly longer than 800 tall.
The font sizes on the Paperwhite are smaller than the equivalent font sizes on the Touch. In the sample screens (attached) Caecilia Condensed size 3 on the Touch is roughly the same as Caecilia Condensed size 4 on the Paperwhite.
If you look at a larger scale of the attached screenshots
, you can see the better font rendering (contrast and darkness) used by the Paperwhite.