Minimal operational clearance: Cross-member to ground?

[66SuperSport]

I've run all of our cars with about 3" of clearance to the lowest points for years without any major issues. Of course all of our headers have hit the pavement from time to time, but this comes with the territory.
The cats on my C-5 are pretty much in the middle of the car, are only 3.25" off the ground, and have never hit.