MAXxed out!

[#1]

Advice sought please.
When I first received broadband (from BT) I was on a fixed rate service and I don't recall too many problems. Then along came ADSL MAX and I was wooed by the promise of "up to 8 Mb". The scales quickly fell from my eyes when the white slab-like Homehub delivered an average download speed of 800 kbps, with frequent (weekly) dropped connections. Eventually, I (metaphorically) ditched BT. in favour of PN. For the first few months, all seemed rosy; the D-Link router supplied seemed to manage at least 1000 kbps download and a rock-solid connection. This changed back in August. My broadband service is now like a roller-coaster ride, with highs of 1800 kbps and lows of 80 kbps and frequent (sometimes daily) dropped connections.
I know I have a long line. I've cut the bellwire, I've fitted an i-plate. My sync rate has increased, but the download speeds keep shifting. I am not aware of any change in the domestic activities in my own home, or that of my neighbours. I do have the local steelworks of course,
Here are my current router stats:
Mode: G.DMT 
Type: Interleave 
Line Coding: Trellis On 
Status: No Defect 
 
                      Downstream Upstream
Rate (Kbps):              2112  448 
 
SNR Margin (dB):      18.1  21.0 
Attenuation (dB):        56.0  29.5 
Output Power (dBm): 12.0  17.4 
I don't have much hair left to pull out. Would I be better off, reverting to a fixed rate product (or should I go the mobile broadband route; the mast is at the top of the hill on the opposite side of the valley with a very high signal strength)? 

[#2]

the attentuation figure is quite high so I wouldn't expect anywhere near 8 Meg (attentuation increases with distance from the exchange due to line length)
I have attneuation of about 59 and get about 1.5 - 2
The first 10 days are the training period where the sync rate is steadly increased to determine your Maximum stable rate (MSR)
You will then find that speed varies by day up to a maximum of the MSR once this is automatically set.
ADSL Max is a rate adapative product so the speed will vary, this is to give you the best performance that is possible from your line.
A word of warning about mobile broadband, in order to get the maximum speed you have to be the only one using the cell (mast)

[#3]

As you have had max for several months the training period is irrelevant.
You appear to have a noise problem on the line which gives intermittently bad synchs.
Is there anyway of monitoring this using the system logs so that you can see when the router loses synch and what the stats are at reconnection.

[#4]

Hi Jim
Just reread the post and assumed that he might have just switched to plusnet (why would anyone use any other)
As far as my understanding goes, when a circuit is migrated the training period starts again which was my basis for the advice.

[#5]

When it is migrated via a MAC (not from LLU) the training period doesn't restart.
He has, of course, had the problem since August after several months with Plusnet   

[#6]

I bow to thee's superior knowledge of the inner workings of BT my dear friend.