Well, I use Brooklyn to contrast with Brigantine and Buena... but the point remains, interference hurts your speed. It also seems to flake-out marginal equipment... i.e., makes them need to be rebooted more often. Interference in Brigantine is not as bad as Brooklyn, but you could feel the difference between day/evening/middle of night and the difference during tourist season versus winter. I would imagine anyone living in an apartment complex or in downtown Southjerseyland would see similar hits if they cared about it... but in a lot of cases, they just buy faster and more greedy (bandwidth-wise) equipment.
As far as defaults, in my experience most routers do not default to channel 6, they default to 'auto'... so they jump around from 1 to 6 to 11 trying to pick the one with the best signal to noise ratio. I just use iwlist to do a site survey, but back in the "old" days we used to do site surveys using a combination of propriety and free tools. The problem is that when you have lots of radio sources, the channels are constantly moving. I swear that whenever I used to manually change channels, it seemed like many other radios would also hop on them.
Of course, in newer routers 'auto' means ALL the bandwidth. That's how 802.11ac gets its most optimistic speed ratings... it hogs up virtually all of the bandwidth in the 2.4 and 5 GHz bands. Sure, its supposed to 'play nice' with older equipment and back off channels it detects others are using, but I question what kind of signal levels trigger this.
Oh, and trying to get a client to upgrade their 2.4Ghz wireless phone is a no-go when they are dead set that our wireless is screwed up.
My original point however, is that if you want speed and have interference, go wired, if you can help it. Most of what I have setup in Brooklyn is hardwired for speed... (at work everything is double wired and bonded for reliability) but its still a PITA when the GF complains about the $250 Wifi router being slow. I need to get serious and figure out how to upgrade her Dell's internal Wifi.
BKNJ