Personally my experience shows that different cables didnt have an affect unless I used a really long flat extension cable, but short flat cables, vs twisted no difference on my line.
Likewise I never notice differences between test socket and normal socket, rf3 filter actually made my sync worse when I had one fitted during my time on aaisp.
There is a lot of fuss about how many problems are solved within the home, but my own experience is problems are caused externally on openreach or BTw equipment.
When I got moved to a broadcom based dslam during my time on adsl which aaisp forced BTw to do, that yielded an improvement. In the adsl days BTw had the usual dual vendor policy, and one vendor was better than the other.
SRA on ukoline turned my line from been unstable on 15db + interleaving to having over a year uptime on 6db + fast path. Ukonline are the only UK isp I am aware off that ever used SRA in the uk, and even then it was a unofficial feature that dan a ukonline staff member implemented as a favour for some tbb users. For me SRA is a massive game changer on adsl, however it seemed difficult to implement with compatibility issues akin to the ECI g.inp problems.
A engineer who turned up on a sunday to fix a voice fault then did something at the exchange to fix my adsl (which also went down), before he did the fix, I had a weird issue where my line wasnt even able to sync at 442kbit, but then the upstream signal strength jumped up to be easily able to manage 1mbit+, I got no idea what he did.
When ukonline ceased to exist, I ended up moving to cable broadband until FTTC arrived at which point I moved back to dsl.
Thankfully for me vdsl has been way more stable than adsl was.