I only have about 2200 books in calibre, but I'm not having performance problems. I'm not sure why you might be affected at just 900 books.
If I'm going to dig through 10,000 ebooks trying to find the ones that I actually want to read, I'd rather do it on something with a better user interface than any ebook reader I'm aware of. Your mileage will undoubtedly vary, of course, and maybe your reader is friendlier than mine, but the thought of sorting books that way on my 505 sends chills up and down my spine.
I'm really interested in what's on that disc, too. Pulps ... mmmm .....