As promised to some readers, we have disassembled an old and a new Airport Extreme N to compare the hardware.

Of course, one can not see the difference when looking at both stations from the outside.

However, when looking inside at the logic board and components, one can easily spot many changes and improvements. The Wi-Fi card now features 4 connectors and as many antennas. So, if you were expecting to run dual band 2.4 and 5 GHz from a previous Airport Extreme N with the appropriate firmware, you will have to forget this idea.
Hereafter are some captures of the Airport station administration, showing the new information and the dual band options:

The firmware pre-installed is the version 7.4, instead of 7.3.2 for the previous models. One can also see the two simultaneous 2.4 and 5 GHz networks, shared and guest networks, MobileMe setup pages, etc.
We will released performance tests as soon as we are done with our investigations.