Interesting how numbers can be so different between tests. I am looking at the April edition of the German car magazine "Auto Bild Sport Cars". There is a test of the M5 vs. E63 AMG, Jaguar XFR and Cadillac CTS-V.
In this test the M5 does 0-100 km/h (0-62 mph) in 3.9 sec and 0-200 km/h (0-124 mph) in 11.8 sec. The E63 does it in 4.1 and 12.6, the XFR in 4.5 and 14.4 and the CTS-V in 4.3 and 14.1 respectively.
The M5 does a quartermile in 11.98 sec, the E63 AMG in 12.07, the CTS-V in 12.49 and the XFR in 12.54
I guess the only thing you can conclude from these tests are that in the specific conditions the cars were tested, they performed as measured. For a powerful RWD car (like the M5), traction is paramount in 0-anything times. And above 100 mph cw value and front area is very important as well, so it's not all power and power/weight ratio.
And Porsches are never to be underestimated IRL, they know something about making cars fast on the road/track, not just on paper
