The global zero-field splitting (ZFS) parameters of three, ferromagnetically coupled, μ3-K3)-[XO4]- (X = Cl, Re) capped, manganese(III) oximate single-molecule magnets, [Mn3O(R-sao)3(2,4'-bipyridine)3)XO4] [X = Cl, R = Me, Et; X = Re, R = Me; Me-sao = 2-hydroxyphenylethanone oximate(2-)], with crystallographic trigonal symmetry were determined by use of inelastic neutron scattering and high-field/high-frequency electron paramagnetic resonance spectroscopy. ReO4- (O…O ca. 1.7 Å) is larger than ClO4- (OO ca. 1.4 Å), which allows more parallel alignment of the local ZFS tensors. However, this chemical modification results in concomitant distortions in the equatorial ligand plane. Consistent parametrization of all spectroscopic data was achieved, and effective spin-reversal barriers determined from alternating current susceptibility data were shown to be in good accordance with the energy barriers deduced from spectroscopy.