o.k., then that's the key step I was looking for in P8 - use hsv exp tone mapping/gain (1.67/1.33) with IDL, and turn off all the shader GC nodes. whilst the manual is not clear on the physical units of how far the raytrace shadow min bias shifts samples away from the posersurface, it appears 0.01 causes self-shadowing on the skin and odd shadow edges on the ground plane (in combination with medium render settings).  at 0.1 those artifacts aren't very noticeable at high-quality render settings.  maybe it's analogous to the displacement bounds.