I don't have either but I think they are around the same size. I'm sure the LV owners of the two will be able to answer it with 100% positivity. I think both are so cute though!
Here, you might find the pictures at this link useful, a girl in another handbag community has placed her pochette collection on display ! http://community.livejournal.com/louis_vuitton/936448.html#cutid1 The only thing about the navona is the brown contrast strip instead of another piece of damier canvas on the side, otherwise I believe it is the same size as the monogrammed pochettes.
Sorry total typo. Meant to type that they do look to be the same size, not "like". Typing too fast and not thinking.
