Channel Mode - If this line says "Fast", you are on fastpath. Otherwise your line is interleaved.
Margin - This is a measure (in dB) of how good your data signal is. Higher numbers are better. If this number drops below 6, you'll start to have sync problems.
Attenuation - Measures (in dB) how much signal loss there is on the line - this should be a low number and in any case should be no more than around 60-65 dB.
Available Bandwidth - Current sync rate in kilobits per second. This is NOT your maximum attainable sync rate.
In the above sample results, the line potential is not revealed to the end user. However, we can examine the SNR Margin and Attenuation numbers. In this case, the downstream and upstream margins are 25 and 31, which are much greater than the minimum of 6. The downstream and upstream attenuation is 26 and 15, which are much lower than the maximum of 60-65. Therefore, this line would likely qualify for a speed upgrade. How much of an increase is possible cannot be known from this data, but these numbers are good indicators.