I agree with you on using the Metallic channel to drive the specular effect, that was my first thought.  I have also used the converter on many occasions to control the glossy; an excellent feature although most of the time I need to color the specular chip a shade of gray depending on the quality of the specular map.  The HVS node is crucial, IMHO.

However, I never drive the Surface channel value that high, I usually keep it very low, starting at approximately 0.01 - 0.015.  If you use this value in combination with a low-resolution HDRI as lighting, you get fireflies in your render.  Most annoying.  As for the Subsurface Radius values, though, those values you provided are too low.  I would use 0.482, 0.169, and 0.109 as a starting point or find other values posted on the web.  Below is an illustration of why I selected those values.

I usually connect a CombineRGB node to drive the Surface Radius RGB values on the PrincipledBsdf node, and as you can see in the image that the higher values give you color tone while the lower values only give you black.  Under these circumstances, the Subsurface Color is providing the SSS tone for the skin.