We can make the ball into a trailer 10 feet away (back of trailer to front of robot). I have a feeling this is further than would ever need to be shot during gameplay.
By decent speed, do you mean balls/second or the time it takes for the balls to get from the shooter to the trailer? (Line drives sure would be fun to watch!) We are firing at about 4 balls/second.
http://www.youtube.com/watch?v=I9wl1x9Wf_Q