I noticed you said a Principled BSDF's Specular slot pretty much handled the Fresnel effect, but I also see that it uses a decimal value, and "0.5 is ok for most things."

If you wanted to use an "accurate" IOR value, does plugging a Fresnel input into Specular do the trick? 

It seems to act the same way, but since the effect is so subtle, I wanted to be sure it wasn't just adding needless complexity or something. :)