The important bits. The 1.6dB noise margin is probably why you have it going up and down, i.e. Sky may have configured the service for too high a speed, i.e. their conservative DLM system was too optimistic on your line.
Shows the sort of speeds you would expect on this length of line, i.e. slightly slower. Solution would be for Sky to tweak the line to run at around 5500 Kbps downstream speed. In theory the DLM should spot this and do this automatically, how often is the router dropping the connection?