Usenet has many things wrong with it, NNTP is not at all designed for distributing large files, it’s for propagating messages across servers. File integrity checks have to be tacked on for instance, and the few servers still serving binaries are commercial services that are vulnerable to copyright trolls.
Classics you don’t even need to pirate there are projects trying to make whatever is public domain available with good formatting like Standard Ebooks.
Top sci-fi maybe try searching prize winners or literary critics as terms, some people have made compilations, otherwise you can make your own compilations and create torrents.