Well you have a sprint button, and the more you increase the fatique bar, the longer you can sprint. However, increasing actual speed? We don't know yet, but be prepared to attract all the pro-attributes folks.
Stamina stat. More we increase it during level ups the faster we'll be. Also races/racial bonuses will probably effect it as well. Lots of possibilities.
no one knows but the devs. and these forums are not going to be much help if it has any thing to do with attributes if you are on the fence about them.