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My maxed out 32gb iPad shows no performance changed to if it were a vanilla one. I don't think storage usage is an issue here, unless all your space is taken in the iBooks app.
 
My maxed out 32gb iPad shows no performance changed to if it were a vanilla one. I don't think storage usage is an issue here, unless all your space is taken in the iBooks app.

Very similar. My 16g wifi is almost maxed out. No change in how it operates. In fact, I add and delete movies frequently when I go on a trip. Sometimes I have a lot of gigs left, others almost none. I cannot tell any difference in performance.
 
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