Actually, the 85 was a great inovation for ti over the 81--it was a steal from the HP-48SX. The 82 was therefore a retro move to bring along the people who were using the 81. The 82 does not include many of the things that were in the 85, as I found out the first day of my use of it. I told my students that I was waiting for the 86 or 87 when the 83 came out, which has vastly improved features over the 82. The 83 doesn't do some of the things that the 85 does well, and the 86 doesn't do some of the things that the 83 does well. The 86 is a more sophisticated calculator than the 83.
What I was really waiting for was the 89--the last of the Eighty series! PS with my calculus students, I use the 48.