Among the seven MECIs, PC-NEVPT2 predicts that 2 is more stable than 1 by 0.15 eV, while all three CASPT2 variants predict the opposite. Among all MRPT approaches, RMS is the only one stabilizing 3 over 2. In any case, the difference between the three CASPT2 variants is at most 0.25 eV, which is in the range of accuracy expected for MRPT methodologies, such that any variant is potentially a valid option in practice.