I don't have a recommendation for this except to buy a dual band adapter at the very least. The adapter mentioned earlier is a good example of one. If you do a search for "usb wireless adapter review" you should find some reviews that might be helpful. If you could ever see yourself buying another router with 802.11ac capability in the near future, you might want to consider buying an 802.11ac adapter.
With a dual band adapter, I suspect that you would most likely run a 5Ghz link between the CGN3 and your pc in order to obtain the highest transfer rate between the two.