Downstream Rate much lower than it should be...

[#1]

I am a new customer of Plusnet Broadband with the Extra Broadband package. My broadband went into service last Tuesday (22/6/2010). However, I notice that it is very slow, and so I ran a couple of tests. All the tests were run by connecting the modem / router directly to the test socket in the master socket; and all the other sockets in the house are not connected at anything. The problem seems to be that the Downstream Rate is much lower than it should be and this sets limit on the IP Profile and subsequently my Download Speed is reduced. I aware that it takes around 10 days after my broadband first went into service for the speed to stablize, but I guess that refers to the IP Profile rather than the Downstream Rate. And since the Downstream Rate is what determines the IP Profile, I am concerned that I will never get anything close to the speed that was estimated by Plusnet when I first signed up. In any case, the following are the results of my tests:
This is what BT ADSL Checker says:
Your exchange is ADSL enabled, and our initial test on your line indicates that your line should be able to have an ADSL broadband service that provides a fixed line speed up to 1Mbps. However due to the length of your line the 1Mbps service may require an engineer visit who will, where possible, supply the broadband service.
Our test also indicates that your line currently supports an estimated ADSL Max broadband line speed of 3.5Mbps.
Our test also indicates that your line currently supports an estimated ADSL2+ broadband line speed of 3.5Mbps. When ADSL2+ Annex M is launched our test also indicates that your line could support an estimated ADSL 2+ Annex-M broadband upstream line speed of 500Kbps and downstream line speed of 2.5Mbps.
According to the BT ADSL Checker, my line should be able to support a fixed line speed of up to 3.5Mbps. This is consistent with the estimated line speed that was given to me when I first signed up:
Estimated line speed:
   3.5 - Checked on 2010-06-02 14:27:19
Current line speed:
   500
However, when I ran BT Speedtester, this was what I got:
Download speedachieved during the test was - 316 Kbps
For your connection, the acceptable range of speedsis 100-500 Kbps.
Additional Information:
Your DSL Connection Rate :576 Kbps(DOWN-STREAM), 443 Kbps(UP-STREAM)
IP Profile for your line is - 500 Kbps
The throughput of Best Efforts (BE) classes achieved during the test is - 9.49:22.78:67.72 (SBE:NBE:PBE)
These figures represent the ratio while sententiously passing Sub BE, Normal BE and Priority BE marked traffic.
As one can see, the actual Downstream Rate (576Kbps) is significantly lower than the speed given by BT ADSL Checker and the estimated speed that was given by Plusnet when I first signed up (3.5Mbps). This is confirmed by my wireless modem / router, which I received from Plusnet last Saturday (19/2/2010):
Link Information

Uptime: 0 days, 0:43:21
DSL Type: G.992.5 annex A
Bandwidth (Up/Down) [kbps/kbps]: 443 / 576
Data Transferred (Sent/Received) [kB/kB]: 0.00 / 0.00
Output Power (Up/Down) [dBm]: 13.0 / 0.0
Line Attenuation (Up/Down) [dB]: 24.0 / 46.5
SN Margin (Up/Down) [dB]: 24.5 / 32.5
Vendor ID (Local/Remote): TMMB / IFTN
Loss of Framing (Local/Remote): 0 / 0
Loss of Signal (Local/Remote): 0 / 0
Loss of Power (Local/Remote): 0 / 0
Loss of Link (Remote): 0
Error Seconds (Local/Remote): 0 / 0
FEC Errors (Up/Down): NA / 0
CRC Errors (Up/Down): NA / 0
HEC Errors (Up/Down): 0 / 0
As I said before, given the situation, I am very concerned that I will never get anything close to the speed that was estimated by Plusnet when I first signed up. Thus any help on this is much appreciated! Thank you!

[#2]

It looks like BT's DLM ( Dynamic Line Management ) system has put you on a 'banded' profile to attempt to stabilise the line.  One of the bands is 288 - 576kbps and the fact that you are synching at 576kbps with a very high SNR tends to indicate that the sync speed is being limited to the top of this band. If its possible, keep the router connected to the test socket and switched on 24/7 and the banded profile should ( Might! ) get lifted automatically.
Has the router always been in the Master socket ?
You say you have other sockets in the house but with nothing connected. You may want to check that the 'ring wire' is not connected to the other sockets as this can cause problems even if nothing is plugged in to the sockets ( see here http://www.kitz.co.uk/adsl/socket.htm )

[#3]

Thank you very much for the reply. I shall keep the router connected to the test socket and switched on 24/7; and yes, the router has always been connected to the main socket. It is only from two days ago did I start connecting it directly to the test socket of the main socket, through the microfilter of course.
As for the Ring Wire, if you are referrring to the orange / white wire that is connected to the IDC terminals 3 and 4 on the faceplate of the master socket, then it has already been disconnected as no wires whatsoever are connected to the faceplate of the master socket. I recall that the BT engineer, when he came over last Monday, told me that since I will not be using any of the other sockets in the house, he might as well set everything up in such a way that the only socket I can connect my phone and router to is the main socket. I hope this is not the cause of the problem. Or are you suggesting that I need to disconnect the ring wires in all the sockets in my house?