Splitting them is the only guaranteed way that they start from the top of the page. But would they still start from the top of the page if it was a printed version? Probably not, or else you'd have a lot of pages with some huge blank spaces.
Group them together. 450 stories, 10 stories per chapter (or per file), means 45 chapters.
Then with 4 volumes, you'd have ~11 chapters per volume. That's much more manageable, I think.
Last edited by DSpider; 12-10-2012 at 08:04 AM.