My SRT only wanted 7.75 qts of oil. That's all we put in any of the 112 motors at work.
All of the modern Mercedes run high capacity oil systems. The V-8 cars usually take 8.5 quarts and we'll slide 9 qts in the V12s.
The pans do have ridges in them. They're designed to work as heat sinks as well as stiffening ridges.
Considering that the twin turbocharged V12 takes barely a quart more than the V6, I wouldn't be too concerned unless you've gutted your car and are hell-bent on embarrassing Elises at the track.