Beam-corrected noise spectra for the WMAP and Planck channels used in this work, rescaled to equivalent 30 GHz noise assuming a synchrotron spectral index of −3.1. The relative sensitivity of the different channels strongly depends on the harmonic scale, ℓ. On the largest scales, the WMAP K band and the LFI 30 GHz channels have a comparable mean synchrotron sensitivity (with, however, a strong pixel dependence, as is seen in Figs. 1 and 2. At ℓ ≃ 800, however, the WMAP Q and LFI 44 GHz are about as sensitive as the LFI 30 GHz channel, and much more sensitive than the WMAP K band.