I think the SA/AS trains were rerouted for a number of reasons including -
Better crew utilisation.
Overnight Sydney/Ettamogah service for ANM Paper traffic.
Excess loading from Melbourne to Perth can be picked up by SA5 and then
double stacked on to MP5 in Adelaide (hence less MP6s need to run).
The reverse at Parkes was very expensive as an army of
signallers/shunters, etc required to split and reverse the train. The
triangle option was priced out of the running.
I believe the running time difference is not very much considering the
safeworking stops required from Coota West to the Hill and the reversing
move at Parkes. From the customers point of view nothing much happened -
it is still a two night, one day service.
-- Cheers Krel"The Universe is not only stranger than we imagine, it is stranger than we can imagine" - Clarkes second law. Railway rules and regulations are the same.