if you want speed and high gas mileage and only have 6,000.00 to spend get a sport bike.. if you know how to ride that is..atleast they get like 28 - 40 mpg and will surely pretty much beat anything on the street.. although then it's really no comparison unless a drag car or another bike pulls upto you.. but hey it's speed and gas mileage and they're cheap
i can find you a hayabusa for pretty cheap