Bad upload speed.

[#1]

That's what's holding back your speed at present. It should be set to 88.2% of your sync speed.
On your previous post only someone very close to the exchange will see the full 20Mbps ADSL2+ sync speed.

[#2]

Your profile updated earlier this morning, so you should now be seeing the difference.

[#3]

Thanks all for help so far.  Post ADSL2+/uncap we seem to have an increase in upstream speed:
0.35 -> 0.85
and an increase in downstream speed:
6.7 -> 11.2
So we have progress! I guess I have one further question:
Why is the router stating the max is 13562600 (and hence an actual attenuated 11200000) and not something in the region of 20000000?
[the router is not doing any speed tests when it reports this figure, otherwise when we were on ADSL1 it would have come up with ~6700000 (our actual speed) and not the reported 8128000. Is it a number given to it by Plusnet on handshaking?]
I understand that the transfer rate will be attenuated, but I'd expect something around 16 if 20 is the ADSL2+ maximum.
I get the figure of 16 from (ADSL1 actual) / (ADSL1 maximum) * (ADSL2+ maximum) i.e. 6.7/8*20

[#4]

the router calculates the maximum speed from the attenuation and possibly noise margin by some unknown algorithm

[#5]

Our SNR Margin has taken a hit: 6 before, 2.5 now. Loop attenuation has increased slightly: 22 before, 23.5 now.
Am I right in thinking that, in these circumstances, the sync speed will drop to compensate for stability?
Can anything be done, or are we at the best speed we can get?

[#6]

The reported attenuation can increase by up to 3dB on ADSL2/2+ because it is calculated differently. Higher frequencies which have higher attentuation are weighted into the calculation.
ADSL2/2+ has 3dB as its minimum target noise margin, and the DLM will use that if it is happy with the line performance. It gives higher sync speeds but the CRC error count may increase.
The main thing to be aware of is that the 21CN DLM manages the connection more aggressively. Leaving it alone to get on with it is the best policy. "Helping" can be counter productive.

[#7]

Thanks spraxyt.  Thanks too to everyone else.  Seems like we're on the best speed we'll get presently. So unless anyone has anything to add, I think that's it for this thread.