I haven't experienced ADSL2, but how are you getting your estimates of speed? You'll rarely get the maximum download speed possible due as you say to varying factors along the way, but my 1500kb/s, at 8 bits to a byte, has a theoretical maximum speed of around 185KB/s, and I usually get around 150. If you really are getting such drastically low speeds and not simply confusing kilobits with kilobytes, you should be having stern words to your provider.
Disclaimer: Don't listen to me, I don't know what the hell I'm talking about.
