There is much more control over SSS with PrincipledBSDF. In the above example I've set  Subsurface Radius to "0.75 0.071 0.071".

In the Blender manual you can find interesting things about PrincipledBSDF and SSS, but nothing really precise about the value for the radius:
"Average distance that light scatters below the surface. Higher radius gives a softer appearance, as light bleeds into shadows and through the object. The scattering distance is specified separately for the RGB channels, to render materials such as skin where red light scatters deeper. The X, Y and Z values are mapped to the R, G and B values, respectively."

Following Blender's logic, however, it will actually rather be a matter of values between 0.0 and 1.0. If you look at PhysicalSurface, values between 0.0 and 1.0 should be appropriate here as well (but not color values). You are probably right that values greater than 1.0 do not make sense. Thumbs up!

---