I have an Apple MacBook Air (Mid 2012 Model), and purchased InSSIDer for it.. Running it on Mountain Lion, it shows my 5Ghz wide SSID with two channels in the chart - but one channel in the graph and says max rate is 75Mbps. If I hold ALT and click on my wireless status, it shows the link speed as higher than that though.

If I run the Windows version on my Windows laptop, it shows the same - only the graph shows the 40Mhz channel, and reports max speed as 450 Mbps.

The above is with an Asus RT-N66U.

Things change, however, if I disable wireless on the RT-N66U and instead designate my Apple Time Capsule as the WAP. In this scenario, InSSIDer for Mac shows the wide channel, and reports max speed as 450Mbps.

Does anyone know if Apple is restricting 5 Mhz 40Mhz client connectivity to only AirPort devices? I know they restrict 2.4 GHz devices to 20 Mhz at the OS level.. But why would InSSIDer show both channels, but report a max speed of 75 Mbps only when connected to the Asus?