A couple of corrections to my previous post.
First, I realized after posting that my statement "including retrieval and processing of title information for the documents" isn't quite true. I forgot that I now lazy-load that particular metadata for each book, on demand (which is also fast.) However, it is definitely true that BaseX is very rapidly finding all of those hits, with retrieval of book-level metadata for each hit.
Also, apologies to Christian Grün for misspelling his last name as Guen in my last post.