Hennessey claims a 124 1/4 mile trap speed for the package although this package on the CTS-V wagon has only done 121. That said, the lighter sedan (approximately 200 pounds less depending on manual or automatic option) should be close to that trap speed. That also should be enough to take a stock F10 M5.
In the video what we see is that the F10 M5 takes the CTS-V out of the hole getting maybe a slight jump on it. The CTS-V comes back fairly strong showing it does have the HP advantage it should but it can not gain any further ground going neck and neck to 124 miles per hour. The M5 holds it off and gains back a little bit of ground lost but then the CTS-V lets off.
A very close run that goes back and forth. The CTS-V shows an advantage in the lower gears but up top can not overcome the BMW turbos and redline. The DCT also certainly helps. If this was a Competition Package M5, it would likely win against the modified CTS-V. An impressive showing for the M5.