Throughput Speed is the maximum speed that could vary  due to the:

1. Number of subscribers online at the same time
2. Number of people accessing the same web sites that you are .

Note:

•  The variance in the max & min transfer rate is due to the 15%-25% packet overhead lost  which is an international standard. 
•  Formula applied as follow  Bandwidth (1- 15% or 25%) / 8