Hi Darren,
I can
only just see NGC5128/Cent.A with averted vision from my backyard with a 6".
If the conditions allow, I can see 5.5mag stars direct and 6.22 averted from the back yard. I suspect Melbourne is far worse.
From a dark sky site however, I can see Cent.A naked eye(averted) with no problems and in 7x50 bin's it's great.
The first pic is of the light pollution over Melbourne:
And for comparison, in the second pic, My house is at the black cross, and the dark sky site I mentioned is roughly where the red cross is.
Both are to the same scale.
BTW, 5128 is listed as mag6.8, but its surface brightness is 13.5! Makes it a bit more difficult
The 6.8 is if all its light were coming from a single point, like a star, instead of over a larger area.