Here's an interesting bit of trivia--at least for the American pilots.
The GS signal is "flight checked" by the FAA only from the FAF inbound down to DA.
In other words, if you couple the autopilot to the GS outside of the FAF (in the USA) you do so at your own peril.
So, keeping in mind what 'mike rondot' says about joining the GS from above, I would submit, if you chose to join the GS from above, *outside* of the FAF, it should only be used for *advisory* purposes and NOT be used to control your descent.
I'd recommend making that descent on V/S to altitude pre-select, until the aircraft is fully established within the service volume of the ILS.