Mike ..... there was very interesting and very informative discussion about bushings about a month ago. You might be able to find it with a little digging in the archives. I learned a whole lot from the discussion.
To make it short, the big lesson for me was to always measure your pen with calipers ... and then use that same measurement for turning your blanks. The caliper measurement is the important factor. The bushings should serve as a rough guide.
As a matter of fact, it was that discussion that inspired Don Ward to write that great tutorial on How to Make Bushings!