For single layers of SiO2, Nb2O5, and Ta2O5 that are deposited by plasma-assisted reactive magnetron sputtering (PARMS), we present measurement results for basic optical and mechanical properties, in particular, optical index, intrinsic film stress, thermal shift of spectral transmittance, and microroughness. We find high refractive indices combined with low intrinsic film roughness, moderate compressive stress, and almost a vanishing shift, indicate high potential for the production of high-performance optical coatings. The high thickness accuracy and process stability are exemplified by the measured spectral performance of multilayer stacks with about 200 single layers.