In this case and the fact we only have 11 WiFi channels it may be time to consider moving to a router with 5GHz channel support.
I'll keep it short since it's like shouting in a crowded room. It's going to be slow and painful.
http://en.wikipedia.org/wiki/List_of_WLAN_channels shows that in NA we have all of 3 non-overlapping channels. And with 11 WiFi networks, it's going to be a mess. I do not expect this to work well.
So this leads me to think it's time to consider the 5GHz WiFi solutions.
This problem has been going on for a couple months: When my notebook is hardwired to the wireless router (Netgear N900 WNDR4500), speedtest.net shows around 25 Mb/s...as expected with Comcast Boost. But when connected wirelessly, speedtest.net often shows 1 to 3 Mb/s...terrible. I get the same terrible results at both 40 feet from the router and 3 feet from the router. Normal wireless downloading results from speedtest.net would be 10 to 15 Mb/s.
I want to keep this short: But I will mention that I have a second Netgear N900, both with the latest firmware, both exhibit the same terrible performance. Until a couple months ago I didn't have this problem with the N900. (I live in a condo complex with 11 other WiFi networks visible.)
Both my notebook (a Toshiba Portege) and my iPad 2 show the same terrible results.
What's the most likely cause?