The Cadillac CTS-V features the Hennessey HPE650 package which is a bolt on package including a tune good for roughly 566 horsepower to the wheels. The CTS-V and the GTR are making similar power but the GTR routes it to all four wheels with a dual clutch whereas the CTS-V does not have a dual clutch (manual or automatic) and sends power to the rear wheels.
The C6 Z06 features the LS7 7.0 liter V8 readers likely know well and it can put out some big naturally aspirated power. The modifications are not specified so exactly what this Z06 has is unknown. What is known is that it is the lightest car of the trio undercutting the ~3800 pound GTR by almost 700 pounds.
The run from a stop should obviously favor the GTR with its all wheel drive. To make it easier on the rear wheel drive competition the GTR does not launch but just rolls into the throttle. It still pulls the other two easily who appear to let off.
The second run is from a roll and the CTS-V can not play due to traffic (don't try this at home). The Z06 shows its weight advantage here getting an early lead but the GTR quickly makes up the difference and pulls in the higher speeds. It is apparent the GTR has a significant horsepower advantage pulling several car lengths by 150 miles per hour.
The roll on between the Z06 and the GTR has the Z06 quickly giving up after the shift where the DCT of the GTR dominates it. If you are wondering why dual clutches are taking over this should illustrate how quick and consistent the transmission is. No user error here, the Z06 is demolished. The Z06 decides he wants to try again after this out of second gear but it's just another beatdown.
Finally the CTS-V gets to play with the GTR from a roll but it doesn't fare any better. This just goes to show how fast even a mildly modified GTR can be.