* Some of my Categories to land on Pages.
* If we land on a Page, (use page2cat to) show the page. In this case, do not show the posts.
* If no Page has been associated with a Category, list the Category as normal.
For this to work I had page2cat return a value rather than printing "Archive for...." and used the return value to determine in index.php what to do (show the posts or not).
Works like a charm.
Happy to share the details if there is interest.