RC should be right with his info. But at the end I think we will meet somewhere in the middle. This means the CLS size. Since CLS is a bit bigger than the E Class and 5 Series, and smaller than the S Class.
Something must be wrong with the picutre, since the GT3 looks as it is standing behind a Maibach, and those sizes we will only see for the 5th or 6th Porsche Modell. Or do anybody really believes that Porsche is not going to do a S Class in the future?! The only question is if they do it before the Porsche (BMW)1er or after.