There's an E90 that parks near my house sometimes that's lowered about that much.
Predictably on our roads, the front bumper is smashed to bits and hanging by a thread. People just don't think about things when they lower a car that much. My car is stock with about 3" of ground clearance, and I have to be careful all the time.
Yes, it's the same on the CTS-V, even at stock heights, I have to be careful. I see slammed out cars all the time, but I just don't see the point.
In most cases (unless you know what you're doing) lowering has the opposite effect of making the car worse to drive.