CL55 vs. CL600

I own a W140 sedan and am looking to purchase a CL. I'm looking at 2000-2002's. Are there any appreciable maintenance reliability or cost differences between the CL55 and the CL-600? Also, how do those two models compare to a base 500? I'd prefer a 55 or 600 unless they are a HUGE increase in maintenance cost or are appreciably less reliable.

Thanks in advance,
Leon