BT Infinity speeds not reaching the quoted through...

Question

Hi, I'm after some collective advice (and maybe even some help) on my BT Inifinity connection.
Firstly the facts:
I live roughly 682m (in a straight line)/1.3km by road from the local exchange.
My BT INFINITY Cabinet is roughly 0.48km on foot (possibly twice the distance when taking the copper cable length into account).
On ADSL 8mb: IP Profile of 7mb with a throughput of 6.95mb maxed with Hub 2 sync'd at 8mb.
On ADSL 2+ 20mb: IP Profile of 17mb with a throughput of 16.5mb ish with Hub 2 sync'd at 19mb (BT Quoted me 13mb on the broadband checker)
(I Know ADSL is a whole different kettle of fish compared to Infinity, it's merely an example of how well my line copes with broadband)
On 20/09/11 I had BT Infinity installed. The Engineer didn't tell me what speeds to expect but I knew from the conservative BT Infinity checker i should get at least 32.7mb (DOWN). My upload is maxing out at just over 8mb (quoted at 6.6mb by BT). I showed the engineer a speed test i did then and there with him in the room - the results are as shown: (35.8mb Down and 8.14mb Up)
http://speedtest.net/result/1492182858.png
I was chuffed, even more so when it rose by the end of the day topping out at just over 36mb with the same upload speed. http://speedtest.net/result/1492351342.png
3 Days later my connection dropped and my throughput was showing as 32mb. I put this down to the DLM as i was still in the 10 day training period. But since then it hasnt changed and my IP Profile has been set at 33mb. On day 11 i power-cycled the modem and then the home hub but still no luck. 32mb is by no means nothing to be snuffed at but it seems speedtest.net is showing my speed wrong as i found out when running a test on BT Speed Test which showed me my Ip Profile of 33mb, but only acheiving a throughput of 30mb! So much for the "Your download speed should be: 32.7Mb". 
So, i don't know if my initial higher speeds where my true speeds given that my line is very stable or if what i'm getting now is the best i can get and i got my hopes up for thinking i could still get much better than what BT quote me.

Answer 1

Update:
Short Version: There was a 10v surge on my line that was causing my connection to be unstable.
Result so far:
http://speedtest.net/result/1528755806.png
http://www.pingtest.net/result/48425777.png
Long Version (Probably TL;DR so i apologise in advance):
Last friday I accidentally yanked the power lead out of the vDSL modem while trying to replace a dodgy Ethernet cable on my wife's PC - The Home Hub 3 is on top of her desk with the OR modem mounted on the wall above it.
As quick as i could i plugged the power back in, and it proved to be a godsend. My dsl light would flash, go dim and it would do it a few times before going solid green for about 10 seconds and then it would repeat. After a while I phoned Technical Support, who diligently read from their script and got me to check all the cables including the RJ11 from the modem to the phone socket - all while the dsl light was doing it's thing. It was irking me cause i had already gone to the trouble of diagnosing the cables and i knew it had to be one of two things; Either my line or the OR Modem. I perservered with the Inidan lady I was speaking to (She was being nice to i'll give her that) before she ran out of tricks and escalated my case to BT Wholesale and would contact me in 1-2 days to see if my connection was working.
Annoyed that she was about as much use as a silent movie to stevie wonder, i went back to trying to get my modem to connect which only got worse when the hub wouldn't recognise the modem being connected. The broadband light would come on as a steady orange after a failed connect attempt, but no PPPoE activation. I thought "great now my hub has gone up the tube".
Eventually after 7hrs i had enough, i unplugged both the hub and modem and took a five minute breather. I then started with the vDSL Modem, plugged in the RJ11 lead and plugged the power back in and low and behold, after a few tries the dsl connected. I gave it a minute just in case my modem was giving me false hopes. After seeing it had successfully connected i then plugged in the Hub and let it cycle through to the orange broadband light at which point i connected the infinity cable and got it all working again. I had reconnected at 30Mb/8Mb and thought the nightmare was over.
Next day (Saturday Morning), my modem had dropped to 22Mb/8Mb with an IP Profile of 24Mb and figured this was normal seeing as i spent 7hrs without any connection. I held my tongue and put up with it for the rest of the day.
Sunday Morning my modem had dropped again and  reconnected at 20Mb/8Mb with an IP Profile of 22Mb... i was not happy and i still hadnt heard back from BT. Fortunately i got a call from BT Wholesale who then asked me what the problem was (an Indian guy this time - do we not have UK Call Centers anymore???) and so i told him, and through his thick accent i manage to discern that he had booked me an Engineer for the next day (yesterday).
Engineer turns up - A quiet Indian guy who asked me what was up and told him, and while he listened he acted like he just wanted to get done and go. So i left him to it. Credit where credit is due - he did a line test (both socket and test socket) and didn't find anything wrong and said he would go the cabinet and have a look see. It turns out there was a fault with my line but he was almost done for the day and passed it onto another engineer who was actually quite chatty, polite and a joy to talk to. He knew what was wrong and confirmed it with me, plugged a test device in to the phone socket and shot off to do his thing. 10 minutes lates he comes back and does the line speed test with his gadget (i have no idea what its called). While talking to him to he showed me what the gadet was doing and showed that my line is capable of 44Mb/15Mb - lolled. He told me i can get the full 40/10 but i didnt hold my breath. He told me what he was doing next and what would happen every step of the way. he rang me to tell me my IP Profile had been reset and it did right as i was talking to him - he was even curious as to what i would get. He told me it would take a while for my speed to increase and happy as pig in smelly stuff i thanked him whole heartedly and waited as i was still stuck at 22Mb but i had a ping of 21 on speedtest.net... i new my connection was vastly improved. Pingtest showed a ping of 18!.
Today (tueday) still working and as i found out the hub 3 has this problem of not updating the speed. I had to go into the settings and "disconnect" the home hub but NOT the modem and reconnect and low and behold fast internet again. 37.5Mb/8.2Mb with a download speed of a steady 4.4mb/sec topping out at 4.5Mb on occasion and spiking sometimes at 4.7Mb/Sec.