I have a mid 2010 iMac 21.5'. I am curious and i want to ask does the iMac support the 5 Ghz 802.11 n standard or only the 2,4 Ghz? In system profiler there is no information about that.
My 2007 iMac supports the 5 GHz 802.11n standard, thus the 2010 should as well.
While connected to a 802.11n network, hold down the OPTION/Alt key while clicking the AirPort/WiFi icon in the Menu Bar to see, what channel you are using.