The router might not be helping. The v1 is VERY old... and was never an ADSL2+ router out of the box.
Netgear released the upgrade via software which never appeared to work great on some lines.
If you can try a newer router such as a v4 (skip the v5), or a broadcom-based router like the Billion 7800N, you might get better rates, however....
13Mb at 36db seems quite optimistic.. but does depend on the quality of the line (and the equipment used).