The CL is faster, or at least seems faster in the real world. The problem with the 400E is that when it is not floored it's tall first gear makes it seem slower. It can be a mind thing as well, I am still not used to such a hard accelerator, when I push it I feel as if I'm fighting with the car to go faster. The CL has the 5-speed which is the difference. I actually sold the CL a while go, it was junk. That list is off all the cars I have owned.
1992 Mercedes-Benz 400E
2002 Mercedes-Benz ML500