"It is beginning to look like I will have a budget of 2-4 min per frame." Well, that sounds like a workable budget, depending of course on what's required of the scene. Think about what you can and absolutely can not do in post too. Much of the time, video post is the answer to shaving down rendertimes even more... the more you can get done in a video FX compositor/editor, the less you have to do for the render, and the more time you save (usually). It can really help your budget tremendously. What do you use for post? Something like AfterEffects or Combustion can really be useful tools for "faking" a lot of things you might normally try to do in the render, and the results are just as good, if not better.

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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.