Difficult to answer to be honest. My old Draytrek router started to go a bit bonkers after 5 years, but it still worked with adsl fine and was only replaced when I switched over to zenís big deal and got a free FritzBox.
If you are suspicious about future router problems it might cheaper and easier to replace cables, filters/faceplates first.
Zen: 77mb down - 20mb up
Stechford (CMSTE) Cab 50