I have Internode ADSL at work (1.5Mbps, 32GB data) and at home (512Kbps, 16GB data) and would recommend them. Good, no nonsense service, and SA-based. I'm waiting for ADSL2 in Norwood (my office is on The Parade) but it will not be available until later this month (actually, just looked, and from their site, I think you can place an order now).
Make sure you have a reasonable data allowance (most of the budget ADSL providers allow something like 500MB which really only gives you the capacity to do very everyday stuff, like no online gaming, no Torrents, no Shareaza, no grabbing XVids from IRC, etc).
As for the speed downgrade, I'm not sure how much you would lose, but ADSL2 is fast enough that it shouldn't matter. I've seen a chart on the Internode site that plots speed vs distance from an exchange. In Kensington Park, I'd expect the difference to be minimal.
One of the reasons for the better prices are that ADSL2 will come through Agile whereas the rest is limited by Telstra who are money-loving bastards and maintain pricing that limits competition, IMO. I started with Telstra in the early days of ADSL but changed because the service is crap.
