Actually, I'm not going to do either one. I'm not concerned with any kind of between real-world kinetic energy and HERO Damage Classes. There may be a coincidental relationship, but I honestly don't care and don't think it's at all important.
The only thing that's important is approximating the real-world lethality of an attack or weapon, and the real-world lethality isn't a simple matter of kinetic energy. KE is a **factor**, but it's not the only factor by any stretch. KE is only part of what determines the degree of damage done to, well, a chunk of rock. Angle matters, material composition matters, shape and structure matter, etc, etc, etc.