Ok cool

So the good news is that everything is working as intended.
In the 2.4GHz spectrum, due to the low number of non overlapping channels, there is a standard for when 40MHz channel widths are allowed to be used and when they are not.
There is a formula (which I can't find right now), but basically it decides how much of an impact you using 40MHz will have on your "neighbours". If the impact is too great, it disables it (even if you set 40, it will down rate to 20MHz).
If your customers are in a less congested wifi area, they'll have no problems getting full speed.
People in apartments or town houses are the ones that typically experience this the most.
This is a great informative article about the subject.
http://www.smallnetbuilder.com/wireless ... ghz-part-1
The "option noscan" does exactly what it says, it disables the router from checking for neighbouring networks. Which is illegal by FCC regulations, but good for testing like in this case
