I've the same issue. my line get 62.5 Attenuation where as my 4 neighbours get 57 ... all with BT Broadband ADSL2+, home wiring all isolated, same cab, same route to the exchange etc. Upshot is that I get about 1.7 download neighbours get 3+. The BT wholesale checker say that I should expect between 1-3.5 this seems such a wide margin that you could drive a coach and horses through it.
The margin really needs to be this wide to allow for differences between routers (individual devices not just models), filters, modem leads, etc., (even before you start taking into account local noise sources). If you haven't already tried replacing some of these things, that would be a good starting point.