For exterior use KNAUF sells and recommends AquaPanels...
And they are available for both indoor and outdoor use, about the plasterboard on the facade in the recommendations of the manufacturer said nothing.
103_3 If the price is not an issue: choose Knauf aquaPanels for the facade or similar panels from other manufacturers, but only for outside work.
As an option: fasten the foam and on it a special putty + mesh + surface putty. That is, according to existing technologies Knauf, Cerezit or similar manufacturers.
Magnesite board tempting option, but this is a fairly new material, as it behaves over time, I do not know.
Of the facade materials siding wooden or plastic.
I like the wood siding, although it requires constant maintenance.
I myself plan to use plastic siding, because at a height of 6 meters I paint at least once every 3-4 years.