Michael has good knowledge on this subject and I'm not debating his answer, but I have experienced an interesting speed anomile...I'm in a "Verizon 4G zone". The map implies I should get 4G anywhere in a 10 mile radius of home. I do not. I'm lucky to get 3G at home.or at least that is what I thought.l get 3gb of data every month, my phone auto-sync's and my gf plays casino slots almost every night from my hotspot. This uses about 2.5gb per month.
Last month she bought a used iPhone 4 and was told it could be unlocked using iTunes online...she tried to do this while using my hotspot. The phone started a "download" and said it was a stolen phone and gave the owner information. She ignored my phones data warning and used 2.7 GB of data in less than 2 hours on the first of the month. I had all month to ponder how the phone was able to use a months data in 2hours...apparently the iPhone was attempting to cloud recover all the pictures and files from the iPhone as FAST as possible. How,??? Who knows. She returned the phone to the very happy owner, she lost the $60 she paid, and I had my data locked off for 29 days just like Michael said. So "theoretically", the data speed is controlled by the powers that be, and is pretty damn fast if they want it to be.