51db attenuation should in theory allow about 4mbps connection. But you also have to consider signal quality (SNR).
Note that the SNR will automatically deteriorate when you sync at a higher speed, because you lose some of the error correction capability on the line when you increase the sync bandwidth (more bins/tones used for data)
Note that the SNR will automatically deteriorate when you sync at a higher speed, because you lose some of the error correction capability on the line when you increase the sync bandwidth (more bins/tones used for data)