The pads are made the same it's just that as you move up to 7.5/8/and 9" pads you need to be real careful about what your doing.
It's easier for the rotary to get away from you and working with a larger diameter pad and it's easy to misjudge how close you are to delicate parts like trim,mirrors, etc (don't ask me how I know).
If you detailing a SUV or truck with large body panels they're great. Body lines on most cars today make using larger pads harder when trying to avoid mistakes. You also have to make sure you put down enough polish so your not buffing dry when you start.