babis3g wrote: You need to use a wired pc for testing download speed and see if still slow down browsing
Via wifi is not stable for testing, more far from the modem's antennas, the lower speed will be (apart the actual speed is coming to the modem may be more lower)

However i can see the snr margin (from the stats) is gone low to 4db which is not good, have you tried any other adsl filter? or place the modem far from speakers, tv, pc (any electric sources etc
Also place the modem in clear place area where the wifi will not blocked & can reach the devices more easy

50db loop attenuator means you are far from the exchange, sensitive adsl line

babis3g wrote: -Fist No Do Not really extend the cable from master socket to the modem, i would not recommend more than 1-2 meters max long for your line
(the ones from the modem boxes are around 1,8 meter and their quality is ok/good)

Is better to run around the wall (on the floor under the carpet) an rj45 (from the lan of the 2850) as many meters you need (can use up to 100 meters if is a good quality - but don't get so long because some modems don't have so much power to handle it)

-Second use modem code from UK download page 2471201 ... this is the best you can get

-If is behind the tv is better wall mount the 2850 higher than the tv (about half meter at least should be fine from electromagnetic interface & also for not blocking the wifi) ...
OR get a small shelf (random pics) where the 2850 can look nicer & later if in the future you move the modem can add decoration there ... or place the AP
http://rusticlogdecor.com/media/2c99813e573b551ffff8158ffffe415.JPG
http://rusticlogdecor.com/media/Log$20Shelf.$20small.0001.JPG

-The filter may not helps really but is worth having one more

-If leave the modem behind the tv as it is ... you can get an AP (example AP800 as you said) for your internet connection ...but
is better to connect it via lan cable (rj45)
the reason is ... if you connect it via wifi, it will lose 1/3 of the actual speed
example if your poor internet connection is 5mbps, it will give out to clients 3 mbps
This is not fault of the AP800 but wifi extensions loose as general rule 1/3 of signal via wifi (except the lose of signal when far from the AP)...
where wired to the AP(2850>AP800) will get all full speed (then you will only have to deal with more far from the antennas, more lower speed)

-There is an option as well (instead of another AP) for Power LInes (perhaps better if you have other floors) ... is very easy, but personal never involved so you will have to ask or search for it

- I tried to give you all possible options ... but If still have line issue come back