Upstream variation

I have three ADSL2 lines at the same site. The first two are two pairs inside the same drop cable. The upstream speeds have always been very different with line 1 being 560-570kbps and line 2 a mere 440-450k. These numbers have been constant for several years. Moving on to line 3, upstream was always around 500k until recently when it dropped to be nearer to line 2 for some unknown reason.

The three lines have roughly the same downstream sync rate 2800-2900kbps with line 3 being the fastest.

My question why the consistent variation? Why is line 1 so exceptionally good, or line 2 so bad? not sure which. Given that line 3 was in the middle until recently then maybe the truth was �a bit of both�.

Maybe being able to see the full stats from all three lines might help with diagnosis.

It seems they are long lines, so maybe the �worst� pair is on a different E side from cab to exchange ?