The long winter nights will fly by on this one but....he talks pants!!
5* was normally the rank that the big wigs retired into. An ACM became an MRAF, like say Sir Keith Williamson. Field Marshalls were still around, the last one I can think of was Inge in the 90s.
In the US Army he becomes a General of the Army and the last one was appointed in the 50s. But Congress can make a mate up when they see fit.
See:
http://usmilitary.about.com/library/...+star+generals
or
wwwtc.nhmccd.edu/people/crf01/history/defencechiefs.html
Can't beleive I did the search!
Ghost