This is what happened to me. I have 2 lines coming into property. I was using BT, getting 40-42k, decided to move to TalkTalk 40/10 service save few pounds, now syncing at 39,998 on the TT line, as expected. The vodafone business line was around 45k, now 47k, so have I 'robbed Peter to Paul' so to speak?
I was actually surprised when I got my second line enabled, it made zero difference. My guess is it depends if the pairs are parallel to each other all the way back to the cabinet, plus your line length to begin with.
