Coolants that meet Australian Standard 2108-2004 fall into two different categories, Type A and Type B. You will find the type of coolant printed on the bottle. The main difference between the two is: Type A engine coolant contains antifreeze/antiboil coolant with corrosion inhibitor, while Type B engine coolant contains corrosion inhibitor only. In other words, Type B contains no glycol (antifreeze). This info is straight from the standard which I have in front of me.
Type B is the stuff you will often see labeled "for pre-1984 vehicles only". Type A will have a higher boiling point and lower freezing point due to the glycol. Note that there is no requirement for the premix Type A stuff to have a certain glycol level. This is for the manufacturer to determine.
There are other requirements to meet the standard such as pH, glassware corrosion levels, coolant hose immersion test, etc. One of the ones you can test yourself is foaming. If you shake the bottle of coolant, any foam that forms should disappear within 5 seconds.
I don't want to make recommendations because everyone's situation is different, but any Type A coolant with a glycol level of 33% is 'probably' going to be fine for normal street use in typical Australian conditions. I wouldn't run the Type B stuff because of the lack of boiling protection, especially if you like to give the car a good thrashing.
Nulon are fairly transparent about their product, which I like. You can see a comparison of their coolant's test results and the relevant standard here (click on specifications in the link): http://www.nulon.com.au/products/Long_Life...trated_Coolant/
Some people swear by the genuine Nissan stuff, others swear by Toyota coolant. Or perhaps you have an aluminium radiator and run the red stuff. Do your own research and decide what's best for your Skyline.