The news is all bad for you regarding Armidale. For starters, getting there via Tamworth there is a hill (Moonbi Range) that is possibly a little more taxing than your South Eastern Freeway. However once you are at Armidale the run down to the coat is no steeper. The difference in that road is the bends and the width of the shoulders (the bit between the white edge line and the safety fence.) Even if you come up the coast you will get hills north of Sydney that are a bit less steep but no one worries about those because they are shorter and much straighter.

If you are not going to learn to drive the type of country between Tamworth and Armidale to the coast you are going to miss a lot of nice country between Melbourne and Cooktown. If your rig is well balanced it is capable of travelling all the roads from the ranges to the coast. They are all semi-trailer routes so they more than wide enough for your rig. The curves will limit your speed far more than the gradients. That just means that you travel slower in lower gears for the few stretches with the steeper gradients. Please learn to drive these routes and become a more competent driver (I consider that a driver is not really competent until they have the confidence to drive this country without worrying.)

It may take a few more cups full of fuel to drive the same length of road with hills than if it was flat. You will use many 10s of litres of fuel travelling hundreds of kilometres to dodge a few hills. You will also be constrained to a few boring roads is you dodge hills on the eastern side of the country. A few years ago I took a convoy of vans up and down those hills to get around flooded roads from Kempsey to Coffs Harbour. Many of those had been previously warned off travelling those roads. Each of those rookies wondered what was the fuss about travelling those roads after we got back to the coast. If you are confident about getting your van down from the Eagle on the Hill then you are half way there,mall you need now is the confidence to steer around the corners.

I welcome you over here to our country and enjoy the scenic mountainous country. You will see something different to your also wonderful flatter country. You will get so much more from a round trip than if you go up and back via the boring coastal route.