Ok this site is really unique, all praise CA3LE, he has done a great service to the internet testing world.... Most of the site you visit are using like 500k files... This means that for broadband internet connections you are really testing your burst speed... 500k isnt even a sweat for most cable or dsl connection.. but with the 1492kb test file you are taxing your connection enough to make it really accurate... If you have ever download anything in IE or Netscape you know what I am talking about.. The first few seconds are like 800kbs... then is falls off... That would be your burst speed... Of course the best way to test you speed is to find a huge file like some 50 or 100 mb file on a really fast server... I think that Microsoft update place is a really good test bed for this...
The reason that you are able to score 3700 on a 3000 line is because you ISP has extra bandwidth and your modem isnt capped at 3000... As more people join you will see your speed go down However, most people will test above the package speed about 99% of the time... Unless you live in like Chicago where the service and speed is slow...