I think both cars do what the were created to very well. I havn't driven the CLS55 either, but the E55 is a great sedan.
I would hope that the CLS would be even more dynamic than the E55, but it will never offer the same sense of connection and involvement of a 997s.
I'm sure that it's been said many times before, but comparing the two is basically comparing a sporty car to a sports car.