The speed is increased 50%, and why not, it's the crusade-meachics after all, and the armies are filled with a bunch of folk who really want to go somewhere and get mad if not so 
If you want to edit it open descr_campaign_db in the data-folder (I use Notepad++ for it which is a shareware, but normal Notepad might work to) and change this:
Code:
<crusades>
<required_jihad_piety int = "1"/>
<max_disband_progress float = "0.5"/>
<near_target_no_disband_distance float = "4.0"/>
<disband_progress_window float = "1"/>
<crusade_called_start_turn float = "1"/>
<jihad_called_start_turn float = "1"/>
<movement_points_modifier float = "1.5"/>
</crusades>