Peter, off hand, I would suggest lowering the shading rate in Firefly to around 0.4 to 0.2, increase pixel samples to about 4, and use gaussian post filter (not box) set to a size of 2. I often reduce bucket size to around 32 (from the default 64) to ensure the render doesn't choke up, but that doesn't have an effect on quality. Some people like to turn on texture filtering for hair, but that can slow the render quite dramatically and cause other complications with skin textures.

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Tools :  3dsmax 2015, Daz Studio 4.6, PoserPro 2012, Blender v2.74

System: Pentium QuadCore i7, under Win 8, GeForce GTX 780 / 2GB GPU.