Here is a handy checker to give you approximately the maximum speed your line can achieve on ADSLmax services.
http://212.23.23.177/calc.htm
You need to enter your current adsl speed
512K = 512
1meg = 1024
2meg = 2048
You also need to enter your Line Attenuation and SNR margin reported by your modem/router
*Note SNR Margin is sometimes called "Margin" "SNR" "Noise" "Noise Margin" and is shown in db.
It is pretty accurate for what my line is currently synced to the exchange now based on the figures i got before i got ADSLmax
For a good ADSLmax ISP i recommend www.nildram.com