I use both the GEBlibrary on my computer and the bookshelf at ebookwise. So I went to each bookshelf and downloaded from there onto the card. There were no duplicates - I went over the list pretty closely.
And you're right - 124m is plenty of space. My concern is that it doesn't do me as much good having a 128m card if the books somehow expand on it and each book takes up more space than on the 64m card. Kind of defeats the purpose, don'tcha think?