Looking at the side taper of the CLR and LS 430, it doesn't seem there is much there.
For example, here is the LS 430 :
Mercedes designed that car with one goal in mind - low drag.
It's hard to believe that they would skip something so obvious if it made that big a difference.
( I do find the angle of plan taper on the C-111 to be quite excessive at the rear. Again,
surely the engineers at Mercedes knew what they were doing and wouldn't have fuddged this up. )