In a really busy area, what's the issue there? If there are tons of people on 1/6/11, you may as well hop into the middle bits - there's already plenty of interference going on in the usual channels.
With 802.11g you're actually taking up four channels out of the available 12? So people hopping in the middle are messing with people on both sides of them. Sorry for the mobile link. https://en.m.wikipedia.org/wiki/IEEE_802.11g-2003
However, if the 'standard' channels are already congested, people are already messing with each other. Look at the semicircle graph on your link - someone on channel 4 is messing a fair bit with someone on channel 5, and a little bit on 6. However, someone on channel 6 is messing a lot with another person on 6.
So, people on the same channel silence each other (CTS/RTS), but on other channels it is simply seen as noise. If there are lots of people on 1/6/11, you're going to spend a lot of time silenced.
It's one of those things that you just have to try out in your own particular circumstances. Will you get better performance if frequently silenced, or better performance dealing with a high level of 'noise'?
