Hi,
I have had Sky Unlimited for about 6 months now and in this time I have had many different connection speeds ranging from 18mb to 9mb. I have no idea what happens but sometimes the router will disconnect and then reconnect at a slower speed.
The thing is though is that this does not happen often. Could be at 18mb for 3-4 weeks with a perfectly stable and fast connection, and then I would check the router status page and it would be at something like 9mb. Then I could check 2 weeks later and it would be at 17mb.
When the internet is on, there are no drop outs and I receive a very stable connection. It just almost feels like Sky are turning it up and down. They also say when I call that I have a good line and that I should be receiving the top end speeds, yet every time they cannot give me an answer.
Here are my router stats, it is exactly the same on my test socket: