This latest article by ByThom is interesting:http://www.sansmirror.com/articles/equivalence-in-a-nutshell.html
Especially this part:With small medium format: ISO 3200, f/8 at 1/125, 135mm lens
With full frame: ISO 1600, f/5.6 at 1/125, 100mm lens
With APS-C (DX) crop: ISO 800, f/4 at 1/125, 70mm lens
With m4/3: ISO 400, f/2.8 at 1/125, 50mm lens
With CX (Nikon 1): ISO 200, f/2 at 1/125, 35mm lens
Looking at this it is obvious why I like full frame. I almost always try to shoot at ISO 64 and if I can't, I try very hard to stay below ISO 400. I hate noise. Also, in many circumstances, I love a narrow dof.
Here is another good article on equivalence:https://photographylife.com/equivalence-also-includes-aperture-and-iso