`CPK' is a combination of both `Bonds' and `VDW' in that it draws the atoms as spheres and the bonds as cylinders. The resolution and radius can be modified independently. The radius of the sphere drawn in CPK mode is by default smaller than the sphere drawn in VDW mode, but this radius can be made larger. Since a sphere is drawn for each atom, it will always be slower than the VDW option, but we will work on performance for future versions. If the values for a sphere or bond attribute are too small, then those objects will not be drawn.