Opinion for a Pocketbook

I mean to try a pocketbook but I use a lot the popup dictionary while reading, so I was thinking: is it like the kobo? And: is the font size and line spacing of the pop up window of the dictionary, customizable (at least with a patch like the kobo).

A second worry was: does the pocketbook handle well big PDF (for example 50 MB)?
And then: which is the responsiver/faster model? (The basic 3 seems quick but has the popup dictionary like the kobo?)

many thanks