R3.5 is good for adealide plains (recommended is 2.5) and I'm not sure that bang for buck the actual benefits of putting in more than 3.5 will give you much (aircell or other).?
You will also have sisalation, and 3.5 on the ceiling should be fine.
Personally I'm not the biggest fan of relfective style insualtion, becasue with dust it does degrade and will continue to do so for the life of he product.
Get a bit of sisalation - stand under it in the yard - it works - slash mud on it and do the same - it gets a lot warmer.
I feel that any reflective style product - such as aircell - is more suited for areas where you cannot fit normal bulk insulation.
Insuation is basically the effecive means of trapping air and stopping it moving - reflective producst add to this benefit - while they are still reflective.
F/G is my short for Fibre Glass.
Hope this helps.