Depends on how you gear them, a Honda CRF450X can get to 150 km/hr with the right gearing. As you gear for higher top speeds you do loose bottom-end power though. We do a lot of desert riding with mostly soft dunes and some flat sections, top speed does not always mean faster times as gearing too high will cause you to struggle in softer terrain. Have a look at the profiles here, will give you an idea.
