Billion modems are only really good if the copper twixt the exchange and you is in good condition -- as soon as the line noise or impedance starts to go up (which is more than likely considering the age of most of the Telstra network) your maximum bandwidth takes a nose-dive.
Where I live, we are 1,900-ish metres (cable length) from the exchange, on a TPG DSL2+ circuit. We also have three different DSL2+ capable modems here, a D-Link (I forget the model, it's packed away), a Billion 7402, and a Netgear DG834. The quality of our copper pair is considered average. Without doing any tweaking, the Netgear is the best performer at 12.1M down, the D-link in second place at just under 10M, and the Billion trails behind at a rather sad 6.2M, that's half the speed of the Netgear. The Billion actually does slightly better if I force it into DSL1 sync, when it gets 6.8M (of a maximum of 8M).
Here's a tip to see how good your telephone lines are. First, dig out your maximum download speed from your modem and jot it down somewhere. Next, visit
ADSL2 Exchanges and enter your address -- you will be told not only what exchange you are connected to, but the estimated distance from the exchange, and also your theoretical maximum speed via ADSL2+ sync. The further apart the estimate maximum and the real maximum as reported by your modem, the worse your copper pair is.
For my money, it's hard to beat the humble Netgear DG834, which you can pick up for $70-ish, as it has an excellent track record for holding decent-speed connections over even some very crappy lines.
