I've probably killed enough brain cells in this exercise.
However, I think that I can better reproduce the quality of the assets in TG which was my goal. I did as Matt suggested and used just the image maps in the default shader slots with good results. I also used the functions without the image maps in the default slots (except for the albedo map), also with good results. Tempting the fates, I used both the default image slots as well as the function slots for specular and displacement. Finally I added one more example which had a higher displacement multiplier. To my eye the images are pretty close, there is a detail blow-up of the area in the asset that was my comparison point and honestly I really don't see much difference. The simplest solution to just use the default shader slots is probably the best (easy beats complicated
. here's the breakdown:
Example A: Using only the image slots in the default shader. Albedo in color image slot. Specular map in reflectivity slot, no roughness image, roughness set to .8. 'Bump' map in Displacemt image slot, did not use provided displacement image.
Example B: Function driven (mostly). Albedo in default shader color image slot. No specular image in reflectivity slot, roughness image connected to roughness function. No displacement image in displacement image slot, 'bump' image connected to displacement function.
Example C: Dual map use in Specular and Displacement. Albedo in default shader color image slot. Specular image in reflectivity slot, roughness image connected to roughness function. Displacement image in displacement slot, 'Bump' image connected to displacement function.
Example D: Same as Example C except for higher displacement multiplier: .67 to 1.5. Higher multiplier on Example A distorted the texture.