They are functionally the same. The 4K was a 4K Mainly due to the 4K camera. Other differences included a different arrangement for connecting to the GUI, and the presence of a "hot shoe' camera mount. And different colored plastic.
To use the CG03 on any other Q500 requires use of the pigtail that plugs into the back of the CG03, and then plugs into the port on the bottom of the Q500.