(I’m sluggishly upgrading from C4 to C6, and have installed C5 on the way.)
I remember quite a lot of complaints on the forum when C5 features very important to some users appeared with such big alterations in C6 as to almost render C6 unusable for important parts of their work. Without trawling through old posts, the only examples I can bring to mind at the moment are transparent events and comping. (I believe the latter problem was resolve by Steinberg’s making something similar to the C5 procedure available in C6.5(?).)
So, I’ve been wondering whether any C6 users habitually dip into C5 because they still find C5 better than C6 or C6.5 for some types of work.