The maxbotix sensors are accurate over long distances (VERY accurate) but only if they are held still. They also have a noticeable lag time along with an overshoot-then-leveling-off issue when used with the analog (I'm not sure if the digital connection has the same problem).
I would consider combining two sensors. The ultrasonic for longer distances and the sharp for closer in where speed is important.
Sharp does have some longer range rangefinders (1.5m) that might work:
http://www.robotshop.com/sharp-gp2y0... campaign=jos