The dependence of the separative power of Iguassu gas centrifuges (GCs) on the rotor diameter and velocity of rotation above m/s is investigated. The separative power is calculated exploring numerical modeling of the gas dynamics and diffusion of the binary mixture in a strong centrifugal field. The separative power is optimized on five internal parameters of the GC: pressure at the wall of the rotor, feed flux, temperature drop along the rotor wall, friction power of the waste scoop and radius of the baffle of the product chamber. The optimized separative power does not depend on the diameter and grows with the velocity as . Optimal values of the internal parameters do not depend on the diameter except optimal pressure, which is inversely proportional to the diameter squared. The optimal pressure grows with velocity as while the optimal feed flux is proportional to . Enrichment of the product flux does not depend on the velocity and diameter in the optimal regime of exploration. Growth of the separative power with is determined by growth of the feed flux with the velocity.