magu: Not really. Attainable Line Rate is only achievable under perfect planetary alignment, atmospheric conditions and hell-freezing-over scenarios.
It's the theoretical speed the modem WOULD get if there was no noise/interference/etc on the line.
I thought that the maximum attainable rate already took those things into account and that the only reason it would be less is if they are limiting the speed at the other end of the connection..
The other odd thing is that the upstream rate is actually more than the so called "maximum attainable rate"..