MGSP+ IV embeds the gauge and flavor structure of the Standard Model into the modular variational framework. It introduces effective modular spectra for up, down and charged-lepton sectors, together with modular energies for gauge couplings and mixing matrices, forming the first version of a “stiffness atlas” for SM parameters. The paper shows how gauge unification tendencies, flavor hierarchies and realistic CKM/PMNS patterns can emerge as consequences of modular stationarity, preparing the ground for the full global fit performed in MGSP+ VII.