Cool thread
From my experience, subdirectories are much less important than the html filename itself. You may want to change the underscore to "-", Google doesn't like underscores as separators.
Which one gets more PR ? It depends on the incoming links only, not the directory.
In general, on-site optimizing has become much less important, that's why all those huge site networks. Link popularity is the key, you certainly recognized many linksites changing their button links to category specific textlinks. Some sites that rank good for a certain keyword don't even have the word on the actual page, but many incoming links using this keyword as anchor text.