Weird. It was the same old engineer, who told Janet that there was absolutely nothing wrong with the line and that it was her modem (despite the fact that modems were swapped before the first callout). And guess what - the problem has now been fixed!
Live sync rates:
#1: down 3015 kbps, up 522 kbps 3 dB downstream ; 6dB upstream SNRM
#2: down 2577 kbps, up 529 kbps 6 dB downstream ; 6dB upstream SNRM
#3: down 2844 kbps, up 386 kbps 3 dB downstream ; 6dB upstream SNRM
#4: down 3012 kbps, up 557 kbps 3 dB downstream ; 6dB upstream SNRM
So line 2 will go a lot faster when I adjust the downstream SNRM to be 3dB, the same as the others.