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[#1]

[#2]

ADSL2+ Up to 20 Mbps - depending on distance from exchange.
Because of your distance from the exchange you can only get 11,897kbps which gives an IP profile of 10,000kbps hence 9.6Mbps speed test

[#3]

[#4]

Read about it here http://www.kitz.co.uk/adsl/max_speed_calc.php
You could look at your internal wiring to see if you can improve things - try the test socket for example
and look at this graph in relation to line length from the exchange

[#5]

OldJim beat me too it.
If you really want to know why have a read of this (and related articles): http://www.kitz.co.uk/adsl/adsl_technology.htm

[#6]

[#7]

Definitely try the test socket for starters. I once re-jigged the wiring at a friends house and sync speed went from ~1.5Mb/s to 3.5Mb/s. Admittedly I think that was an extreme case, she had many old extensions going no where with many junction boxes.
Personally I recommend getting the proper NTE5 faceplate (NTE2000) and forgetting all those hanging filters. That way you eliminate reflections from the bell wire and other wiring artefacts.
http://www.run-it-direct.co.uk/BTNTE5ADSLfaceplate.html
Steve

[#8]

Quote from: JamesM

my attenuation dropped from 30 to 29 when I was switched to ADSL2+

It's just measured differently across different frequencies.
So not comparing eggs with eggs. 
That said, it's common for the ADSL2+ result to be slightly lower than the ADSL1 one so your result is entirely normal.

[#9]

[#10]

Why can't you move the router next tro the master socket and then cable or wireless from there

[#11]

Even if you can't put your router next to the master socket permanently (perhaps your wife/gf doesn't want it on the hall table!  ::)) it would be worth connecting it directly just as a test. You may find there is no improvement in which case you can feel satisfied you aren't loosing anything.
If you must use a long RJ-11 cable make sure it's using a twisted pair and not one of those flat telephone extension cables.
Steve

[#12]

[#13]

Did you try the test socket

[#14]

[#15]

Quote from: JamesM

I just went and bought a 10m Cat 6 cable, so now my router is in my hall and plugged directly into the master socket and 10m of ethernet cable to my computer. My new stats are sync speed 10006 Mbps, down from 11897. Once again, it doesn't make sense.

It does makes sense - your test has shown that the connection from the master socket to the modem was not presenting a bottleneck. Slight variations in sync speed are to be entirely expected, particularly at different times of day and when making frequent (dis)connections. Remember with ADSL we are well into the stage of squeezing every last drop of bandwidth possible out of an infrastructure that was not originally designed for it and hence as such we have to expect not to necessarily get precise consistency of results.
Mathew