Hi
Its quite normal for SNR Margin to fluctuate during the day - normally it decreases in the evenings...
A decrease over a period of days then back up again after a re-connect is a bit more unusual and could be router/firmware related... although because of just how variable SNR can be its often quite hard to say.
If you get a better SNR Margin from the test socket then that is indication that you would benefit from and adsl NTE5 faceplate. Like you say the downside is location of the router near the master socket. However if you wish to re-locate elsewhere then that means another cable. This should still in theory be better than running on a normal phone extension cable since the 2 signals are separated at point of entry in to the home and you can also buy better quality cable for the adsl connection. Theres a couple of the regs on these forums that I believe have done so, so they may well chip in on their own experiences.
------------
Looking at those stats your output power has actually increased a little... (mine also did when I got maxed, but not everyones does.
I and someone else have wondered in the past if some routers are "lazy" until pushed to the limit.
Those stats looks pretty good and much better than most max estimators would have given based on your prev line stats. Even Saffy's which is what I consider gives the best guesstimate normally comes out with a throughput of about 3.5Mb.
I notice those were morning results and you will have to see what happens over the next few days and how much your SNR Margin fluctuates - particularly in the evenings when its more likely to be affected.
But otherwise things are looking pretty good.
If it stays around about where it is... then your maximum throughput is going to be around 5Mb.
At 6208 kbps you are right on the borderline.. if you can give yourself a higher SNR Margin then the next stage is 6240 kbps which will give you a maximum 5.5Mb throughput.
But at least where it is now you have a bit of room for fluctuations since your sync speed could drop down to 5696 kbps without any changes being made to your bRAS.
I think if I were you I would observe what happens over the next 3-4 days and see how stable your sync rate is.