Hi beamblack,
In answering this, I will say it applies to anyone who is going on FTTN or Fixed Wireless.
When you connect to the NBN, start off by connecting on the sandard speed plan. Do not ask for a speed boost to be applied when you apply to connect.
Once your connection is active, check your modem and see what the maximum line rate is. This will tell you what your connection can connect to the Node at.
Then do a speedtest and see what your throughput is. If on the 25/5 plan, your are gettin gover 20Mbps throughput, then apply for your speedboost. If you are getting speeds that are much under this, then call up and report the speed issues. You then wait until Telstra purchases more CVC from NBNCo and it is implemented.
Once the speeds on the base plan have increased, and you have decided that you actually need more spped (most people don't really need it), then apply to get teh speed boost added to your service.
Even if you are the end of the line length on the NBN, you should be able to get 50Mbps. The absolute worst case is 25Mbps (and I would consider you very unlucky if you ended up with that).
When an area is first connected, there are usually congestion issues, so that is why I recommend you hold off on the speed boost to start with.