I favor the copy method, because importing would cause issues of redundancy AND, most significantly, it would bring in old stuff that's now unwanted. However, it would bring in everything!
I'm not clear how to copy from one to another. I am able to open one or the other by renaming the files so that the one I want Outlook to open is outlook.pst.
gurutech, you say "open both files in Outlook". How?