Right in the middle of all my experimenting....
Unit HP 16G Intel i7 3.6 mhz 
Image 1 before update MPD 0.6 AA6 Render time 18 min CPU did not check usage performance
Credits: Rock right cube rock with displacement pipe after default shader, color function surface shader WASasquatch clip fantasy granite light.
            Rock left cube rock with displacement pipe after default shader, color function surface shader WASasquatch clip Dirty marble shader, scalar 10
tree Blender 2.79
grass masonpappy file share 
fake stones mhaze 
cave guy Manuel Bastioni Blender plugin Getting to know expressions and  Blender Hair Tool on wide open mouth guy
Garb Blender cloth/collision fabric sewing through animation simulation / Blender Hair Tool curves mesh ribbons fur  
( In the middle of all of this I am trying to parent , with data transfer method weights, the garb to the avatar so clothes do not split apart when posing) 

Image 2 after update 
path tracing on surfaces enabled   Render time 1 hour MPD 0.6 AA 6     100% usage  but ticked right along with no lags
Disabled avatars
Changed scalar dirty marble clip to 5  I will probably take that down to 3