The E55 is markedly quicker than the M5 in a straight line.
M5s run 4.8-5.0 seconds to sixty and low 13s in the quarter mile.
E55s run 4.3-4.6 seconds to sixty and mid 12s in the quarter mile.
I think the M5 is still quicker around a road course, as it has superior handling.
As for the Video, that Cobra is not stock. In the original match with the E55, they quoted dyno numbers of around 480 hp at the rear wheels for the Cobra. If those power numbers were correct, it should have beaten the E55, which is represented as stock (other than drag radials). I don't know if the Cobra driver is just not very good, or if the Cobra is having mechanical problems, because a 480 RWHP Cobra should be able to take the E55.
From my own experience, the 03 Cobra is not very good on a road course. Driver skill makes a huge difference, but I let one by at Road American in my NSX. I shouldn't have let him by, since I was all over him and left him shortly thereafter. The minor advantage he had in straight line speed was easily overcome by the vastly superior handling of the NSX. Again, I don't know how well he was driving the car.