For a series of FeIV=O complexes with tetra‐ and pentadentate bispidine ligands, the correlation of their redox potentials with reactivity, involving a variety of substrates for alkane hydroxylation (HAT), alkene epoxidation, and phosphine and thioether oxidation (OAT) are reported. The redox potentials span approximately 350 mV and the reaction rates over 8 orders of magnitude. From the experimental data and in comparison with published studies it emerges that electron transfer and the driving force are of major importance, and this is also supported by the DFT‐based computational analysis. The striking difference of reactivity of two isomeric systems with pentadentate bispidines is found to be due to a destabilization of the S=1 ground state of one of the ferryl isomers, and this is supported by the experimentally determined redox potentials and published stability constants with a series of first‐row transition metal ions with these two isomeric ligands. FeIV=O complexes with tetra‐ and pentadentate bispidine ligands were studied regarding the correlation of redox potentials with reactivity for substrates in alkane hydroxylation, alkene epoxidation, and thioether oxygenation. The redox potentials span about 350 mV and reaction rates over 8 orders of magnitude. The reactivity difference of two isomeric pentadentate bispidine systems is due to destabilization of the S=1 ground state of one of the ferryl isomers.