>> The first one is - does the connection rate change automatically at the exchange/router
No, it needs a resync.
However there does appear to be a time when the router/exchange will automatically resync, and thats if your target SNR changes via the DLM change after a period of stability to decrease your target. This is not the same as an IPprofile change.
Dont reboot the router too often as you want the DLM to think your line is stable. If it the IPprofile then may be easier to check via the BT performance tester.
>> The upload connection rate for the Belkin is usually 384 where it was 448 on the Home Hub until it fell away to a current 416
Upload should be 448kbps. Its the standard upstream connection speed for maxdsl. Upload frequencies are at a lower range than downstream, and should be unaffected by what goes on in the downstream range.
The usual advice is to check your internal wiring/filters/ringwire etc as you have already done.
>> My noise margin (down/up) used to hover around 5.8-6.0down/6.0-7.0up. It is currently sitting at 12.2down/6.0up. (Does the noise margin come down automatically first and that allows the connection rate to improve itself or is it the other way round?).
It looks like some instability (or perhaps too many disconnects has fooled the DLM into thinking the line is unstable) which has increased your
Target SNRM.
If the line is stable for 14 days, in theory this should drop back down in 3dB stages.
Each 3dB of target SNR will be costing you anywhere between 400-1200 of sync speed.. but as your line is long... probably more like 400kbps.
When the target SNRM comes back down - this is the time mentioned above in my first paragraph, where your line will reconnect automatically.
