Measuring Airport connection speed?

How can I check the spped of my Airport connection? And what is a normal speed to expect? I currently have Verizon DSL 3Mps service. Recent checks have shown I am downloading at anywhere from 2.3-2.7 and uploading at about 0.2 to 0.4. My wireless connection is quite slow – in fact, much slower than it was six months ago. It has taken as long as 45 minutes to download an iPad app, streaming is often impossible, and pages loading frequently stall out and have to be re-loading all over again. Verizon claims the problem is my equipment. At first, they said my computer was running slow. But, after I pointed out to them that this problem occurs on six different devices, they changed their tune to say it was a problem with my Airport Extreme. I use my network for a five year old MacBook Pro, five year old MacBook, iPhone 4, iPhone 1, iPad 1 and iPad 2. The speed does not change with the number of evices on, whether 1 or 6. Also, my sister-in-law has had the same problem occur with both her personal PC and her work PC. I need to check to see if the problem is indeed, with my Airport. I have both an extreme and an Express to extend the range. So, to get back to my original questions: How do I check the speed of the connections of my Airport Extreme and Expres? And what sort of number should it be putting out? If the problem is my Airport, I need it either fixed or replaced. If the problem is not my Airport, I need to know that information so that I can get back to Verizon. Thanks.

Both computers are running OSX 10.7.5. The iPhone 4 and iPad 2 are iOS6. The original iPad is on iOS5. The original iPhone is whatever latest OS it will run.