Spectral rendering, part 3: Spectral vs. RGB

Now that we have a spectral renderer, it is time to see if it was worth the effort.
I hope you agree with my reasoning in part 1, that RGB rendering does not match the physical reality, but does it really matter?
We will now compare RGB rendering to spectral rendering using my spectral path tracer.
In the process, we will look at various types of light sources.
RGB rendering simply multiplies RGB triples of illuminants and textures component-wise to arrive at the linear RGB color displayed on screen.
Spectral rendering uses proper illuminant spectra (mostly from LSPDD.org) and reflectance spectra that are upsampled from sRGB using Fourier sRGB.