Well, @Rizvan's
test is best case speed, over a short period of time with no history. The question of how long will it last full speed is really about the number of bytes that your ISP has agreed to give you each month. This is
*not* bandwidth, and most ISPs don't really enforce "bandwidth caps" because bandwidth is by definition instantaneous.
What the ISPs actually do is enforce traffic caps. If you move more than X gigabytes per month, we will charge you Y dollars.
From a network design viewpoint, monthly traffic caps are silly. Caps over an hour are far more important to the engineering of the network. Most real users of computers only ask for things like video streaming for a couple of hours a day, so its pointless to talk about caps when folks are sleeping or at their day job. Even at work, most folks here are computer folks, often programmers, and we have code to write, we can't spend the whole day watching videos. So the real world traffic cap is must lower than 24x7 times the number of days in a month.
I have a 1 MB/s up and 10MB/s down link that I pay for as a business line. I pay for, and get, much higher traffic caps than most consumers want or need.