As I have already mentioned, contention is the issue with my fluctuating speed. The cabinet is oversubscribed which is not Sky's fault, it is BT Openreach's as there is insufficient capacity to deliver maximum speed at all times.
I was one the first to upgrade in the street to FTTC and could solidly get 76Mb/s throughput but now approx. 5 years have gone by the speeds can be half that at peak times.
There appears to be a misconception with broadband speed (as do most of my customer's & being a Network Engineer) that speed is yours to have at all times. This is not true. Liken your speed to a motorway and in the early hours of course I can set my cruise control to 70mph and because there are no cars on it I can have all of the bandwidth (speed) available however, during peak times I'm lucky if I can get up to 70mph as the traffic speed constantly fluctuates with load/volume.
Shawrey