Well my sync speed seems to have settled at about 5mb
From the stats you posted you should get 10-11Mb. I am pretty sure one phone call to Sky could get it sorted out, but if you have made up your mind to go, there is not much point.

As Paul says just ask for your MAC, don't say anything about cancelling. If they say you have to cancel to get it, tell them they are talking rubbish and should read the regulations.