It only takes 300 megajoules to vaporize a human as opposed to 3 Gigajoules; which is actually the energy required to atomize a human.
Taking that new formula, 300 MJ * 4 = 1.2 Gigajoules of energy or 1,200,000,000/4,184,000 = 286.8 kilograms of TNT equivalent. Building level or 8-C. Still a lowball, but this will scale to the fodder tiers again; Marines, Hydralisks, Zealots, Zerglings AP, ect.
Note: Might be late, but apparently, Psionic Storm is atomization and the old calc might be applicable after all.