Thanks BoredEngineer for the additional information.
Dual paraboloid maps for point lights sounds like a good optimation possibility for this technique.
Regarding the artifacts: I don’t know how severe these would be, but I imagine that they shouldn’t be so drastically, since I only need low frequency diffuse color from the sky and ground to fake global illumination.
As far as I know it is not possible to use the dynamic scene capture render target as a source for the skylight cubemap. I could use it in my materials, true, but then I break the PBR conversion, which is guranteed when using a skylight.