What Rathji said. I have a dual band and it smokes on my only dual band supporting device, my iPad 2. However for your single band devices, Use this free browser app to see what channel your neighbors are using:
http://tools.meraki.com/stumbler
My neighbors were all on 6 or 11. So I set mine to channel 1. Major improvement.
The problem with having a router auto select the channel, is that they almost always set to 6 or 11 until there is way too much interference.
Manually setting the channel may require you to change it now and again, but it is worth it IMO.
I think it is worth at least a test to cycle through the channels, and retest download speeds.