Well the connection rate is usually proportionate to the wireless signal, and while connection rate itself doesn't apply a bottleneck, wireless signal problems that cause the connection rate to drop can cause performance issues. It has to do with spatial streams but its all very complicated. Wiki would do a better job defining it. Not going to lie, troubleshooting wireless performance issues is kind of complex.
I think the easiest way to define the problem is walk around your house and look for places your wireless drops abnormally. I'm not talking the basement of course, but areas in your house where you should get good signal and you don't. This might point out any interference causes. Some interference might be too subtle to effect signal levels, so you might want to use speedtest.net too and run some tests in places you normally have your laptops and then one in the same room as the router and compare. Then use inSSIDer and look for congestion on the particular wireless channel you are on. Then if you do see congestion, I will show you how to change the wireless channel or perhaps even enable some advanced wireless settings to get around the problem.