Welcome to the site :cool:
Be sure and go to your User CP and update information relating to your location, type of riding, etc. After that grab a spot on the couch and tell us a bit about yourself. How long you have been riding, what kind of riding you prefer, where you are located, etc. We will do our best to hook you up with some fellow dirt bike enthusiasts.
Regarding your question, there are many variables that affect the terminal velocity of any motorcycle. Gearing, horsepower, terrain, starting point, etc.
For example the TTR will achieve a far higher speed if you ride it off of the rear ramp of a C130 at 25,000 feet than it will on your average piece of mother earth. TTRs are not designed to be speed demons, rather a good solid bike that will allow folks to learn the basics of dirtbikes without breaking too many bones.
BTW - They make fantastic pitbikes so don't ever sell yours. Keep it around, you will be glad you did!
Again, welcome to the site, and shout if you have any questions!