Do I need to create 2.4 & 5GHz networks manually with dual-band Airport Extreme?

"when you setup the router, you have a choice of creating one network per frequency or one singular ssid that supports both frequencies. in the former, you manually select which network you want to use. in the latter, the client device picks whichever it supports.

see http://www.engadget.com/2009/05/01/how-to-set-up-dual-band-wifi-and-juice-your-downloads/ for a clearer explanation."