We've currently deployed using the three non-overlapping channels 1,6 and 11.
I read a post recently on a forum where someone suggested that they use channels 1,5,9 and 13 in Australia (which is where I am also). Although the channels overlap, the overlap occurs on the channel 'tails' only. The poster advised that these channel tails can overlap without having a negative impact on the performance of the wireless network because the channel 'centres' are still 20Mhz apart.
This allows for the use of 4 channels albeit with channel 'tails' overlapping.
I would like to know people's opinion on this topic. We're still running channels 1,6 and 11, but would consider moving to 1,5,9 and 13 depending on the feedback to this post.