In relation to making a pie-menu.
I've tried finding research on this, but to no avail.
My reasoning is this: Put the most used features at the easiest places (although putting opposites.. opposite each other (i.e. Undo & Redo)).
I suppose this might vary between different pointing devices, but that's not a problem. Separate statistics for different ones would be preferable.
Mouse and touchpad are probably the most used ones, although I can still accommodate for others as well (trackball, pointing stick ++) in the software's settings. ("Using a trackball? This is probably best for you")