For instance, the ASUS (RT-N16) says "IEEE802.11n Draft" and can run DD-WRT. Can a firmware upgrade convert it to IEEE802.11n Final, or does that require hardware changes?
If you are purchasing a new router, be it single or dual band—go with an 802.11n router. And not 802.11n draft, which is an older standard.
Instead of products based on a final standard--which should appear by early 2008 and will be Wi-Fi Alliance-certified for interoperability--what we have now is a flood of "draft" 802.11n products based on a preliminary and incomplete version of the standard. These products might be--but are not guaranteed to be--firmware upgradable to the final spec.