To really check your internet speed you really need to ping your server to get an accurate measurement. What you're paying for is the speed from your home to the server, and no further. So using a measurement site isn't giving you a true measurement. If any path from your server to the site you're after is experiencing problems, bad connections, cuts, bad equipment, etc., your speed is going to drastically drop. And if the CRC for what's received doesn't match what's sent, it will be resent. And it will be resent until it checks or times out.
Something else should also be taken into consideration, the site's servers. That site might have the latest and greatest which blaze when downloading. Or it might have those first generation ones which still send one bit at a time. The point being, servers also play an important part in the speed you achieve when visiting a site.
If speed is important then I would first have a talk with my provider, and have them make sure you have the correct speed. If that passed, then I'd contact the site that's slow and explain the problem, what you've done at your end, and how long it took to download this or that product. If people don't let them know there's a problem, or a perceived problem, it may never get resolved if indeed there is an actual problem with their equipment.
Our video card went south and when the new one arrived we received a coupon for a free game from Steam. I'd never downloaded from Steam so the manger had to first be installed. I did notice this particular download was slower than most, but I wan't in a hurry and didn't worry about the time. And, the game will be released April 29, shucks.
If something gets your goat, it just proves you have a goat to get.