Pagerank determine crawls rate amongst other things (http://techpatio.com/2009/search-engines/google/matt-cutts-g...).

I find it is also likely that short URLs (especially in the case of a directory-type site) are seen first by the spider and that this order is respected by the crawler (FIFO).

You can also ask in #seo on irc.freenode.net I know there are knowledgable SEO people in there who might be able to provide you with a decent answer.