A C6 will destroy most older cars - it's amazing what 25 years in suspension progress and 400 horses will get you.
Now if you want to compare a modern race car that's built to a class and a Porsche 917, 935 or 962 - then yes it will be a better fight (mainly because the Porsche 917, 935 or 962 were not built to restrictions.
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"If you can make black marks on a straight from the time you turn out of a corner until the braking point of the next turn, then you have enough horsepower"
-Mark Donohue