"A nice dark, oily coat"
I think most people would tell you that already you are roasting way too dark. Ultimately your choice though.
This type of roast is what wed expect to get in Gloria Jeans and any dont care what the roast tastes like shops.
Climates are completely different all over Australia so hopefully someone will come in and let you know the best timing for that side of the country.
Try roasting at night though for a start when its cooler.