Just curious what the outcome would be in a drag race and a rolling start?

I think the SL would win but it would been very close

The M5 would win both races IMO.

The M5 will win, the SL63 is heavier and although it has better low/mid range torque, when you are drag racing what matters is high RPM power and this is what the M5 has.

The SL63 might stay with it off the line for a short while, but I'd say past 80MPH or so the M5 will start to pull away.

Lets not forget that the SL63 is hooked up to the new AMG DC-7 speedster that I believe, operates quicker and smoother than the M5s.

Would be close, really would depend on the driver IMO.

M

I think the M5 might have the higher ground from a dead stop with the SMG only and being some ~150kg lighter.
From a roll it might be in trouble because of the SL's massive torque.

from a standstill, Im pretty confident the M5 would take off quicker (provided the driver is using the aid of the launch control feature) but from a rolling start I also feel the SL63 would have the upper hand even though it is heavier then the M5.

Is the SL63 faster than the CLS55?

MCT is most probably smoother, but SMG3 is quicker (65ms).

As for the drag race, I feel SL63 will definitely have an edge from dead stop cause of the torque advantage (I am guessing SL63 also has some kind of launch function - if not it is probably even). Also on a drag strip SL63 probably has an advantage cause the high traction surface will help it put down all the torque better. But at +125mph my money is on M5, the last 2 gears on the MB transmission are over drive and is not gonna help.