@MoSs i see it completly different. Both my M6 cp and rs6 c7 are stock. I know for my cars that the M6 cp pulls way better above 200kmh than the rs6.
The water air colling of the m 4.4 Liter is very efficient on High Speeds.
Now if it comes to tunning, pp performance m5 do Runs 25 sec up to 300kmh with blackbox and cat delete. I do think for minor mode that is very good. Despite the fact that the ecu of the m5/6 were not completly craked and the power comes from biggy pack.
For quarter miles i cant speek as i do not have apropriete race track,
but for sure as i stated allready out of the box my rs6 is faster than the M6 due to the 4
Wheel Drive and ultra short low gear Ratio.
M6 keeping up with aventador