The hardiest frangipani species is plumeria rubra. I assume all of the frangipani trees in Melbourne and almost all frangipani trees in Sydney are frangipani rubra.
For people living in and around Melbourne and Sydney, frangipani rubra is a safe option. Naturally there are variations in climate from area to area and even greater variations from position to position (micro-climate). The warmer and the more protected a position, the more likely the frangipani obtusa species could survive or even grow well.
As an example, the temperature in rural areas surrounding a large city like Sydney will drop several degrees colder than the city. The temperature in suburbs far from the coast (West Sydney) will drop several degrees below suburbs near the coast (North Sydney and the Eastern Suburbs). A position which is open to the north and has high building or trees to the south for protection will help greatly too. Materials which reflect the sun’s heat, such as glass or aluminium also help. Materials which store heat such as rock and brick also help.
Will link to Choosing A Position For A Frangipani Tree
Frangipani rubras grow well in South East Queensland. If your selected position is shaded or you want a no fuss frangipani, rubra is probably the best choice. Many people choosing a frangipani for South East Queensland choose or at least consider a frangipani obtusa. Another reason for choosing a rubra is flower colour. There are many flower colours whereas the obtusa is limited to the Singapore White (White flower with yellow centre
Read more about these two options on our Frangipani Species page.
Going north of Brisbane up the coast of Queensland, frangipanis can survive in almost any position and grow more healthily in warm positions. Choosing a frangipani for those areas has almost identical considerations as people in South East Queensland as mentioned above.