Hi Bob and Janine
Firstly I should say that you will thoroughly enjoy the drive through the Kosciusko National Park. It is stunning scenery.
We took our 18.5' (internal) Kedron ATV2 down Brown Mountain a couple of years ago. Prior to this descent, we had been down the Clyde Mountain several times and the Macquarie Pass to Kangaroo Valley without any problems. You just don't let the speed build up and lightly touch the brakes to keep it under control..... I would say though that the descent down Brown Mountain was the most hair raising. But let me explain.....
We have a Tekonsha Brake Controller that has 3 settings, B1 for soft around town braking, B2 for highway driving and B3 for aggresive downhill braking. Someone in their cleaning frenzy (and I shall not mention names in here) must have pushed the button and it was sitting on B1. Hence our trip down Brown Mountain had my knuckles white and my eyes wide like saucers. Half way down when the brakes started shuddering in the vehicle, I pulled over for a breather and to cross myself and ask God to safely get me the rest of the way to the bottom. One quick check of the brake controller told me what the problem was and after changing it back to B3, the trip to the bottom was a breeze.
We we still laugh about this experience and even just the mention of the name Brown Mountain gets my heart rate up. It is several klms of constant downhill. I think there is a sign at the top that tells you exactly how far. But it is no different really than the Clyde. We have found a softer way from Goulburn to Nowra that involves just one, very short hill, and this is the way we cross to the coast now.
I wouldnt hesitate to do the Brown Mountain drive again, as I mentioned the countryside is just spectacular (and you can be assured I would double check and triple check the brake controller settings next time).
Enjoy the drive !