Unless you have a very fast VDSL connection you may not need a better router. 802.11n is not real fast but it may keep up with a DSL connection. You could compare the speeds you get connected via ethernet to the wifi speeds. It is not uncommon to get 50-75mbps on 802.11n but it varies a lot from house to house.
Using a dsl connection as modem only is kinda strange. You most times must still run PPPoE on the router and many times you must have things like userid and password from the ISP. It is not as simple as a cable modem where you just plug the wan port in and it works with the default settings.