Robert_Charlton - 11:00 am on Feb 26, 2013 (gmt 0)
moopy - What you're describing is called "faceted" navigation, and we've had a number of recent discussions about it which take an approach that I think get it right.
Unfortunately, the best discussions start out approaching the topic from a different mindset, using different vocabulary to describe the situation, so you might have a hard time finding them.
This recent discussion, IMO, is the best of the bunch, summing up much of what came before and linking back to the most relevant preceding discussions. It's called "Should I flatten my store's URL structure for better SEO?"... and probably should be called... "Best Approaches to Implement Faceted Navigation"....
IMO, this approach using just one url for the product page (and linking from different category and subcategory pages) is the least likely to create problems.
Note that the thread refers back to earlier threads which discuss breadcrumbs, etc.
To avoid multiple live discussions on the same topic in the forum here, I recommend expanding on any thoughts anyone might have about your hypothetical approaches in this thread... but continuing discussion of particulars of the early February 6th - 13th approach in that thread, still active and noted above.