When an ebook is loaded, at first there is a countdown of the pages of the book,
presumably it is doing some sort of page format alignment. Once that has been done
there is not a noticeable delay in the page turns. As for the page turns speed
comparison between the different formats, I haven't noticed any difference.
This should be true for both the regular jetBook and the jetBook Lite which I use, as
for the most part the reading software is the same, with the current firmwares.
(Adobe Reader Mobile 9.1.1 for ePub & pdf)