killer_uk said:http://www.dslzoneuk.net/checker.php?
I'm pretty sure all exchanges are MaxDSL enabled now. The biggest factor in the line speeds you get is the distance from the exchange. This tool shows how far you are from it amongst other things.
What this doesn't take into account though is the ACTUAL phone line distance, as they don't take a direct route to the exchange. So this is only a very rough indication of distance.