Your bucket size at 128 is rather large if you're raytracing. I recommend lowering it to 64, 32 or even 16 in extremely heavy scenes. Remove back facing polys will affect to things that I can think of: raytraced reflections and transmapped hair - there's hair missing behind the character's right ear. But it will save time by (theoretically) culling half the scene's polygons. A snaazy video card will not help your final renders; it's all about CPU cycles

I like to apply an SSS network to the eyewhites, changing the scatter color to 50% grey.