My theory based on the geometry and inspection of the system goes like this:
The clunk stems not from a metal on metal but from the motion of swaybar and how it is installed. The cobb swaybar is slightly narrower than stock, which means that the endlinks are not completely vertical. In an ideal world the spherical end links would deal with any mis alignment and cause the pull/push force to be lined up perfectly with the end of the swaybar and provide a perfect torsional load to the swaybar. The reality though seems to be that when you hit a bump with only one side (and the swaybar unloaded) the initial motion is translated to a lateral motion of the bar. When the bar curve contacts the bushing it suddenly stops causing the bar and endlink to clunk. Adding the lateral links reduced the motion that can be imparted to the bar, but didn't seem to eliminate it. Solid endlinks might reduce it further, but reports are mixed on that end.