iPlate not compatible - so what now?

[#1]

That doesn't look right but you need to do some more checks:
1) Remove all of the extension sockets and check that the Blue/White& Blue pair is connected to Pins 2 and 5  on each socket.
2) What is the Blue/white wire at the bottom of the picture going to?
3) If you are going to remove the Orange wires from Pins 3 & 4,  also remove them at the extension socket ends and tuck them away safely.
In a nutshell, the Blue wire with white stripe should be connected to Pin 2 at each end and the White with Blue Stripe should be connected to Pin 5 at each end.

[#2]

The spare wires at the bottom look like they are the ones coming from the small junction box in the doorway - the first box the BT wiring goes into. It looks like whoever wired up the master socket used the orange and blue wires to connect to the junction box, so that would explain why there is an orange wire on terminal 5, and a couple of spares not connected to anything.
I also noticed some corrosion on the screw terminals in the junction box - the blue/green corrosion you get on batteries when you leave them in an appliance too long.
Anyway, I disconnected terminals 3 and 4 on all the extensions, and checked that they are all wired correctly, and they are, so now I can just disconnected terminals 3 and 4 in the master socket?

[#3]

OK, the wiring looks correct albeit the use of the Orange wire instead of the White/Blue Stripe.
The corrosion on the incoming terminal is significant and will usually cause an audible crackle on the voice service. The corrosion can be from several causes:
* An Aluminium incoming cable connected to Copper or Brass terminal or copper internal wiring
* Age/ Damp/ spillages or cleaning fluids contaminating the box
* Poor quality cable simply corroding over time.
If you have recently taken over the property and can show that you have had this problem ever since you commissioned the line then you have a good case for arguing that BT should correct the deficiencies and fit a new NTE5 Master socket. It would be best if this could be fitted at the point of entry which is probably where the Junction Box currently is. You would then be responsible for the wiring from that point.
Who is your Telephony provider? They should be able to arrang for this to be done at no cost to you.

[#4]

With BT for phone, so even though the junction box terminals are corroded, i doubt they'll change it for free as there's no problem on the voice side of things.
I disconnected the bellwires from the master socket last night, but its not changed my attenuation or SNR at all. Attenuation still at 47db, and SNR anything between 9db and 12db.

[#5]

Afternoon,
Don't know if this makes a difference to my connection speed, but im now syncing at ~3700 kbps, but I notice that in the High Speed Broadband part of my account settings, that it says
Estimated: 1.5 Mbps on 2009-04-03
Current: 2000
Will this be limiting my actual connection speed even though im syncing at 3700?

[#6]

Yes, absolutely.
We're waiting for the BT Profile to pick up, after which our profiling will also increase and you should then see better throughput.

[#7]

I have a http://www.adslnation.com/products/xte2005.php on my main box. This filters th ADSL signal before it enters your house so no need for often cheap and bad quality filters after the socket.
Get the new box on then use a good quality RJ11 cable not one that came free with your router and try and get the shortest you can get away with plugged directly into the router.
I would leave this setup a couple of days to settle, still probs then its BT's end  and you can phone them with confidence. If not start adding all your other peripherals at least you can narrow down any possible causes inside the house.
In my experience any extensions or connection between your router and the main box just decrease line quality and any changes need time to take effect, constantly plugging/unplugging things will lowe sync.