They're race cars, designed and configured to compete in a class with specific rules.
A COPO Camaro (or a Mustang Cobra Jet or Challenger Drag Pak) could be run in any number of Sportsman, Super Street, Stock Eliminator, or Super Stock classes. Some classes are grouped on power to weight ratio (which is why the engines have very specific outputs) and race on an index, other classes are grouped by weight to displacement with an index, Sportsman classes are bracket racing.
This is the intent of the platform. You can race that 572 with the 430 HP tune in a Super Stock class that's classed based on HP to weight or you could choose to run the smaller LS-based 5.7l with the supercharger in a Comp Eliminator class that runs based on weight to displacement.
How fast can they be?
The chassis are certified to 7.50 and they're just about there.
NHRA has a specific class for the fastest COPO, Cobra Jet, and Drag Pak cars called Factory Stock Showdown. As expected, there are rules: Engine displacement, supercharger displacement, supercharger pulley size, and weight are all factored.
Even with the NHRA holding the leash, the fastest Factory Stock Showdown cars are running 7.6x @ 18x mph.
So, yeah, they're faster than a Demon.