Once he's got a connection between two points he might want to use it for other things, like a printer connection, or computer-computer, or NAS, or video...How is it? The OP wants a link between his router and a computer. The router cannot process data through the phone line any faster than 50Mbps (assuming cable). Why install better than what the router can actually handle?
You can get DSL routers with gigabit ports for well under £100.
Given that a wired link is always going to be better than wireless, and given that two jacks take no more wall space than 1, and given that it's no more work to run 2 lengths of cable than 1, linking the rooms with 2 5e or 6a cables is, IMO, a no-brainer.