A faster router will not speed up your connection. It is dictated by the distance and quality of your phone line from the telephone exchange and the actual service you receive, in your case 2mbps. The biggest difference you would notice is if you plugged the router directly into the main BT socket and disconnected all other telephone equipment (including your Sky box) That will give you the best reading possible for your line. If it is vastly different from what you are now getting then there is a problem with your extension wiring.
Also, make sure that every telephone socket which has something in it has a good microfilter (including your Sky box)