Minor nitpick, I'm not sure if exact match in URL slugs matters from Google's perspective very much. I do read that searchers' eyes can be drawn towards the exact match (which are frequently bolded in the SERPs), possibly leading to a higher clickthrough rate.
It's been a while since I was looking at how google's crawler worked. For items that had multiple ways of navigating there, I remember using the link rel="canonical" to let google know where the page would have been if not for the category information etc in the url.
