Satisfactory DSL connection rate and IP Profile, Poor Download speed

[#1]

Last year for much of the time I had download speeds in excess of 5 Mbps. Nothing has been changed by me with the inhouse connections or the equipment since then.
At some stage before Christmas the download speed started to decrease to 2Mbps and for the last two months has been around 0.71 Mbps

The following speeds have been obtained over the last month using two different routers. The speed has been taken at all times of the day, including some in the early hours. I have used three different speed testing sites. I have tried with a Dell Laptop as well as my desktop and get similar results.
706,706,711,707,713,757,708,708,709,713,714,714,714,710,712,718,714,717,720,721,724,718,697 Kbps
During this time I have used the BT speed testing site and the results below is typical of what I have obtained.
    Download speed achieved during the test was - 813 Kbps
    For your connection, the acceptable range of speeds is 600 Kbps-7.15 Mbps.
    Additional Information:
    Your DSL Connection Rate :7.52 Mbps(DOWN-STREAM), 448 Kbps(UP-STREAM)
    IP Profile for your line is - 6.5 Mbps
The BT speed is nearly always higher than that obtained from other sites
Using the ' ADSL Exchange and Line Checker ' I get the following results
Exchange: Purton BT Code: SSPTN
Location: Station Road, SN5 4EN
Distance:- Direct:    487 metres
  (appx)* By Road: 483 metres
  Status 
ADSL enabled: December 17, 2003
DSL Max enabled:  March 30, 2006
21CN WBC (Broadband) Not available
21CN due : (PSTN) info N/A 
FTTC Not available
SDSL enabled : Not Enabled
  Broadband Access† Market 1
BTw Pricing Band  Band E
BT Line Speed Estimation 
Fixed ADSL:  2048 kbps (2 Mb) 
DSL Max:  8000 kbps (8 Mb) 
  21CN WBC : Not Available 

RAG Test Results 
Fixed:  1Mbps and 2Mbps available
radsl:  512Kbps and 256Kbps available
MAX:  ADSL Max is available
TPON:  No info in database
Check:  The check identified another service on your line which may prevent you from ordering a
new ADSL connection. Examples are : Existing adsl connection, DACs, LLU, TPON etc
I am not aware of any other service on my phone line. I have a BT NTE5 Master ADSL Adaptor for the master socket. Only my router is connected to the ADSL socket. The only thing I have on the phone side is a BT Studio 1100 and a bell.
The Broadband Line Status as shown on one occasion when using my BT Voyager 2100 is as follows.
Line Mode G.dmt
Latency Type    Interleave
Line coding    Trellis on
Statistics Downstrean Upstream
Line Rate 6816 448
Noise margin 14.6dB 26.0dB
Line attenuation 7.5bB 4.5dB
Power output 12.4dBm 13.8dBm
No errors showing
The other router that has been tried is a NetgearDGND3300v2 but I cannot find detailed statistics on that router.
Reading through various forums I see ' capping ' being mentioned. Is this what I have and how can I change that ?
Thanks for any help

[#2]

There is nothing there which shows a problem except the speed tests and your line isn't capped as that limits the sync speed not the throughput and only happens on 21CN ADSL2 which you can't get
Two questions
Does the Current Line Speed from https://portal.plus.net/my.html?action=data_transfer_speed also show 6.5Mb/sec
Are those results wired or wireless
One thing though - your downstream noise margin is high (assumed to be a 15dB default value) and therefore there must have been problems in the past - either disconnections or high error rates

[#3]

Thanks for your quick reply.
All measurements have been with a wired connection.
From the link you gave I get
'  High-speed Broadband

Estimated line speed:
Not recorded (service activated before we introduced estimates).
Current line speed:
0.75 Mb  '
Any further test I can do ?

[#4]

Have just swapped over to Voyager 2100 router so can give current statistics  which are
Line Mode G.dmt   
Latency Type Interleave 
 
Statistics          Downstream        Upstream 
Line Rate              7648                      448 
Noise Margin      11.9 dB          27.0 dB 
Line Attenuation  7.5 dB      4.5 dB 
Output Power      12.1 dBm      13.8 dBm 

[#5]

Your problem is Current Line Speed 0.75Mb which is limiting you.
It would be worth phoning support and asking for it to be lifted to match the BT IP profile of 6.5Mb

[#6]

Thanks. Will try that.