Just looking at the usual oil chart http://ratwell.com/technical/OilSelection/VWOilGuidelines-SE.jpg and wondering what oil is used in Australia as the SAE 40 seems to be used from 20-40 degrees but it drops off lower than that in the evenings but SAE 30 only goes up to about 25 degrees.
Don't forget, the higher the second number, the thicker the oil remains at high temps. I'd say 40's fine for everywhere. 30's too thin IMHO, even in the UK, when the engine's hot.
