You would have to step up on the gearing some. You could get a little faster but the real hold back is you batts. Promod posted a test he did on motors. He had that it takes about 2000watts to run 60 mph. I think the thread name was david vs goliath. I try to find it. That may help you out.
Here is the link iwas talking about.
http://www.rc-monster.com/forum/show...=&threadid=923
Hope this helps you out.