I would like to suggest creating an admin option to sort the order in which posts are displayed in categories and/or tag pages. What I have in mind is something like this:
On each category or tag page there will be two simple drop down menus. One has lists sorting options (for instance, by date, alphabetically, author, etc.). The second is for ascending or descending order.
In addition, in Settings --> Reading one can set the global sort options for categories and/or tags with the same two drop-down menus.
This way one can easily determine the sort order of posts in categories and/or tag pages on a global level while having an override for individual categories and tags.