The price difference was too much for me to jump to Edition 9's. As far as I know, they use the same drivers, so I'll be just content with thinking that my other equipment isn't good enough to utilize the full potential of an Edition 9.
As for the HD-650 and 750 comparison...
The 650 certainly has more bass, and since I got used to it, I currently feel that the 750 is lacking in that department. But we'll see how that changes. After all, the 750 is still burning in, but I see some good potential here.
There is much more high energy with the Ultrasone. To the point where it bothered me right out of the box, but now it's curbed under control.
And in the pictures, the Ultrasone looked pretty small, but in actuality, they are quite big. Not as big as the Sennheiser, but still quite something. But I would say they are still portable.