brains71 that seems most unlikely to me. I also live in queensland and had my home done recently with 3.5 and there is a huge reduction in temperature. The only area not done was garage and it is still hot and the rest of the house very cool. You can even prove the difference with thermometer or just place the hand on the ceiling - the difference is huge.
I do have whirley birds on the roof but direct comparison between insulated and uninsulated reveals the truth. Dont forget to take into account whether the days are hotter as well because if the air is hotter radiated heat from roof is difficult to measure except by direct comparison technique.
