Our is factory fitted and it shouldn't matter much in aerodynamic and range wise. Battery consumption would be more related to acceleraion and driving habit. in the city I get 11.7 - 12.5 kWh/100km so yes should be doable for Syd Can trip on an extended range. If you have luggage I would recommend an after market roof tray to make it easier loading unloading. Just finished its first 1000km so no idea how things will be.

Definitely need bigger boot space I find the front is quite a lot of waste space but decided it's better than hauling my aged hatchback WRX around with petrol price these days. I learn to live with it but roof rack is a must.