Hi there
Since you are living in an apt (like I do), IMO, I don't recommend using 40 MHz channel since it eats up 2 adjacent channels, mainly (1+5, 6+10 and 11+7) and this will cause overlapping with other neighbors which results to the fluctuating speeds that you see on your Windows status connection. In overcrowded situations, I recommend to set your router to 20 MHz only so you won't have overlapping channels like I have on my setup right now, despite having 20 routers in range. This gives me 144 Mbps most of the time which is the maximum I can get at 20 MHz channel width. However, I tried using 40 MHz channel width and it made the speed fluctuate a lot resulting in flaky WiFi performance.
I suggest to read this article as well: http://www.metageek.net/support/why-channels-1-6-and-11/
