split system vs ducted reverse cycle.

The application is for an 2nd story extension. 2 bedroom, 1 study + 1 retreat. The weather is Melbourne type, mild and moderately humid ~30-40%, 25C-35C in summer 7C-15C in winter.
The downstair is running ducted gas heating. There is a 6.5kw split reverse cycle at the back living room.
what are the pro and con vs the following scenario: a) split system, reverse cycle in the bedroom (2.5kw) and study (4-7kw). The study unit can blow into the retreat. with 2 condensor outside at 2nd level. 1 condensor on ground level. b) a 7kw -10kw ~5 points ducted. Install in roof cavity space with 1 condensor outside.
Cost of a and b are about the same. Multiple split system seems to be more expensive than to buy single.
We were thinking to get the inverter type. ie DC motor drive. ie try to buy as efficient machine as possible.
I am swing towards a), less mucking around the insulation of the new roof. Aestheically, it is not as nice with 4 condensors outside the house. Seems to be a little bit more efficient and more control.
But I am really inexperienced in this area. Thanks in advance.
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