The water surface was quite close, thus the bokeh balls didn't get much enlarged. However, the curved surface of the entrance pupil is evident, more so than with the 200/2 if memory serves. The image is cropped as I'm not a big fan of cat's eye bokeh.
In terms of image sharpness etc. the 400/4.5 is amazingly good. Its bokeh performance varies depending on the actual scene and the way you approach it photographically. Most of the time, the background is a very pleasant blur.