Why would anyone be surprised by a Z-28 as described? The CTS-V already has a 6.2 556hp supercharged engine. So there would be no surprise for it to show up on the Camaro.
On a side note, yes, the CTS-V is impressive. But, it does not feel like a car with 556 hp and it is not that big. I was surprised that it feels much smaller inside than my 300C and not that much faster feeling. The Camaro weighs just a little less.