Let me see, let's take the 997 Carrera (not S!) from the same AMS issue as a comparison:

Braking distance to full stop from 190 kph to O kph:
BMW M5 - 137 m
Mercedes CLS 55 AMG - 139 m
997 Carrera - 130 m
The 997 Carrera comes 7 meters earlier to a stop which tells a lot about the braking performance. And this is only the "standard" 997 brake, not the Turbo brake and not the PCCB brake. In the same AMS issue, there is a brake system comparison between different cars and the 997 Carrera S PCCB system "plays in a different class" as AMS claims.

Handling Performance
ISO Handling test:
BMW M5 - 138,5 kph
CLS 55 AMG - 136,6 kph
997 Carrera - 141,9 kph

18 m Slalom:
BMW M5 - 65,3 kph
CLS 55 AMG - 62,9 kph
997 Carrera - 66,8 kph

And from 0-100 mph (160 kph), the "monster" engine equipped M5 and CLS55 gain only around 1 second compared to the 997 Carrera (not S!).

No doubt, especially the new M5 is the hell of a sports limousine, I don't deny that. But it is no sports car.
I owned a E 55 AMG for a couple of months and I really loved it. The engine was powerful and it was fun to see other drivers being surprised about it's performance.
But I realized that I'm "only" 39 years old and I ended up in a limousine like my 65-year old dad 15 years ago. No thanks. The E 55 lacked charisma, something was missing, something "special". And traction was horrible, I can't imagine the new CLS 55 is much better. Not to speak about the CLS 55's optical appearance, I saw two cars in Germany and it looks HUGE, bigger than a Mercedes S class. Ouch.

When I exchanged my E55 with a Porsche Cayenne Turbo, I suddenly felt that special feel again, something I can't describe. But of course the Cayenne Turbo is no sports car, so I'm happy I finally ended up with a 997 Carrera S.

So whoever plays with the idea to go for the new M5 or CLS55, think very well about it and take your time.
Also testdrive a Carrera S for comparison or maybe a GT3.
And if you need the extra interior room (family, kids), you won't be 100% satisfied as I wasn't satisfied with the E55 with two kids.

You want a sportscar? Fine, take a Porsche or Ferrari.
You want to be fast but you NEED a limousine: go for the M5.
But whoever thinks the M5 is a sportscar because it has that kind of straight line performance, should set his preferences straight. I can drive a limousine when I'm 60, right now I want to enjoy life and have fun. SUV for the family (with some extra power and "feel" for Daddy ) and the sportscar for Daddy only.