As Pressman has stated the physical operational benefits of broad verses standard are zero.
The big thing is interchangeability of equipment so let us put broad gauge to History in the context of Victoria and standardise the Country lines so that a goods wagon if traffic dictates can be run anywhere.
If this was 1860 it maybe worth exploring if any advantages in the broader gauge exist but the decision to build Nationally with standard gauge was decided when the Trans Australian Railway was opened in 1917.
There are also practically no engineering benefits of standard gauge over broad. Aside from interoperability with existing standard gauge lines, there is only one benefit mentioned below.
American Railroads may not be perfect but they realised pretty early that break of gauge was not a commercial winner.
American railroads did not need to be interoperable with any railways in England, where standard gauge originated. Most early American railways had gauges wider than standard.
The wider the gauge, the wider the wheelset. Wider wheelsets are more stable at higher speeds and can have a wider chassis/body on top.
And both straight electric and diesel electric rolling stock can also have larger motor within wider gauge bogies, with more low end torque and thus higher gearing.
This is only a theoretical advantage and in practice, modified standard gauge High Speed Rail trains have done 574kph on test runs so it doesn't appear to be a show-stopping issue for standard gauge trains.
How tall and wide are these trains? Maybe it would become and issue if we made them taller and wider.
The other theoretical advantage is with axle loadings. With a larger gauge you have a wider gap between the load-bearing points on a sleeper/tie, so you can distribute the weight across a wider surface area and hence reduce the ground pressure - leading to more room for higher axle loads. Again - a very theoretical advantage. Pilbara iron ore trains seem to do quite fine running ~40 tonne axle load trains on standard gauge track, although I understand that they are getting close to the theoretical limits of their permanent way design.
In case of low floor trams, another advantage is a wider aisle and/or more room for boey movement. Low floor trams, while quite a recent development, are unique among rail vehicles in this respect.
In summary: a broader gauge has some theoretical advantages that are vastly outweighed by the advantages of using a common, system-wide gauge.
That wasn't the case when our first railways were built, because ours have never needed to be interoperable with those of any other country.
Nevertheless, the advantages of having a landmass wide gauge outweighing any advantage of a broader gauge has shown to be the case even among tramways, despite tramways in each metropolitan area not needing to interconnect with those of others.
There are broad gauges other than 1600 mm, just not in Australia...
The English Great Western Railway was built to a gauge of 7 feet 0 1/4 inches, substantially more than standard.
It did provide significant technical advantages in 1835.
In case of GWR passenger trains, it meant a lower floor. Now, while high platforms are almost invariably possible in all locations, and all trains in existence at the time were single decked, it would have been an advantage had the GWR used double decker trains, a lower floor makes it easier to fit an upper deck.
The widest gauge of any track in use today is 5ft6, used a lot in India, parts of South America, and the BART. By the way the BART doesn't need to be interoperable with any standard gauge railways, but their fleet renewal is more expensive that the international average.
Graham4405 you are correct in asking how "much" standard gauge has been constructed in Queensland and Tasmania.Well Tasmania is an isolated system so to convert any lines for uniformity with the mainland would be silly in the extreme.
Let's say that all mainland colonies had agreed to the same gauge, say the Irish one, and Tasmania started constructing its railways later. Would the gauge of the mainland be relevant to Tasmania, at least indirectly?