We still use v8.3 (we've used AC since v1/beta but I don't know what our client number is) as we really didn't want to have to require assistance with every change in hardware in order to proceed without interruption. Also, in our situation we're better off with the bugs we know rather than the bugs we don't. But we have to use a Windows 7 computer for the server, as AC v8 does not work with Win10 as server (keeps dropping connections). This is okay for the time being, as we have paid for continuing Windows security updates, but if we were not going to retire in a couple of years, we would look for something else.
5 stages of grief, huh? :-)