Anyone had any success using a Buffalo wbmr-g54 router for ADSL2+

[MisterW]

As Rik says, Goodness, what a mess, typical BT rats nest...
Well the good news is that the line to the downstairs point doesn't have the bell wire connected, its six core twisted pair cable by the look of it and the orange/wht & green/wht pairs appear to be left coiled ( loosely!! ) up.
The other cables look like typical old style 4 core ( blue/orange/green/brown ) non twisted pair where the line is blue/orange. It looks like non of the green or brown wires are actually connected together, although some are connected to lone terminals, which means the bell wire isn't connected and is good news!. I'm a bit uncertain though about the green & brown wires in the vicinity of the top screw in the picture as its not totally clear whether they are connected or just dangling loose ( don't see how they can be connected since that's just a mounting screw ).
Regarding tests with things disconnected, initially you're only interested in the router stats i.e synch speed and SNR.
I'd start by getting a set of stats , then disconnecting all the other phones, Sky box etc , just leaving the router connected and see if there is any difference in the stats. It's going to be difficult to eliminate any noise pickup from the extension wiring itself because its hardwired and therefore technically BT's jurisdiction and you shouldn't interfere with it.