Can't help with the Australia
bit, but most cables have a 33c designation. However, there are also delux cables and I use the Quicksilver type which are easily available from Mercury
or Mariner dealers. They are slightly thinner, more flexible and much lower friction. So on a power boat
they are a delight to use if you are constantly changing the throttle position.
On a yacht the lower friction will be worth while for a long cable run. You can see the difference in price
on this UK page:
Would I change both? yes whilst you are at it. You really don't want a cable breaking in the middle of nowhere, at night, coming into a difficult harbour.