My guess is that in a large tank, there are a handful of geos that could hold their own, namely altifrons and 'Geophagus' brasiliensis, which aren't really like other geos anyway. I have seen large brasiliensis males mixed with CA cichlids in large community tanks at a local cichlid dealer and they don't seem to have any issues keeping up.
But again, it boils down to your tank size, and stock, and the personalities of your individual fish. I don't usually mix CA and SA unless we're dealing with the smaller, more manageable CA.