  The next generation of Cosmic Microwave Background experiments will produce
cosmic variance limited observations over a large fraction of sky and for a
large range of multipoles. In this work we discuss different consistency tests
that can be performed with the upcoming data from the Simons Observatory and
the Planck data. We quantify the level of expected cosmological parameter
shifts probed by these tests. We discuss the effect of difference in frequency
of observation and present forecasts on a direct measurement of the Planck
T-to-E leakage beam. We find that instrumental systematics in either of the
experiments will be assessed with an exquisite precision, well beyond the
intrinsic uncertainties due to the CMB cosmic variance.
