Although the CL63's blown 5.5-liter can out-muscle its big-block predecessor, don't expect the sharp staccato bark that we know -- and love -- from the 6.2-liter-and-Speedshift combo in E63 and the SL63 AMG. The CL's rumble is a much more subtle baritone.
The AMG car's auto stop-start function works well, restarting quickly enough not to impede take-off. But it's strange how the sudden silence at red lights actually calls attention to itself. Expect in-car conversation to stop as well. The auto-stop feature only works if the transmission is in the C mode (which also makes for quicker upshifts and second-gear starts); it's disabled when the transmission is in Sport or Manual mode.
The CL550 uses air springs, while the CL63 (and the V-12 cars) adds active body control. Both coupes are a bit stiff-legged over bad pavement, the CL63 perhaps slightly more so, and choosing ABC sport or normal mode doesn't seem to make much difference. But the upside is that the CL-and particularly the AMG-exhibits iron-fisted body control. The CL63 has essentially no body roll, and for such a heavy machine (some 4800 pounds) it's also amazingly resistant to understeer.
An Invisible Hand directs the CL, for drivers who can't be bothered to do so themselves
The CL pioneered many of Mercedes' current high-tech features, from stability control (S600, 1995) to active body control (1999), so of course there is a full complement of high-tech features on board here. For 2011, the CL adds a new capability to the previous lane-departure and blind-spot warning systems. If the driver ignores either system's warnings, the car will automatically apply the brakes on the wheels on the opposite side, to nudge the CL back into its lane. Those systems, along with pre-collision braking, are part of the Driver Assistance Package (which maybe should be called the Distracted Driver Package); it's standard on the V-12 cars and optional on the CL550 and CL63.