I really liked what you did with the chase cam in the past because of the movements of the car, but I didn't like the location of the camera itself. It was a bit too low. It would be nice if the camera was just high enough to see what's directly in front of the car.
This R8 video from 2:06 to 2:16 has good positioning, but afterwards, it is too high up.
The following three videos are pretty good for where the camera is located, but it would be great if you could mix these camera positions with the movement you have in the Z4 video. They're all a little different, but they all have a good height and angle relative to the car. The distance from the rear bumper is not too important, but it would dictate the height.
I'm glad this topic came up since I have to use chase cam on a regular basis.