I put the Jet TBS on my 5 SPD GT and noticed quicker throttle response and it really work's on the top end. In my car you can go from 70 MPH to 100 MPH very easy with not a lot of lagg.
I don't feel much of anything on the bottom end with off the line type of stuff. It probably make's I'm guessing about a 3 MPH difference to the wheels.