One other trick I forgot to mention for speeding things up (a little, as in a kilosample or more, scene dependant) is nulling skin shaders that are also hidden by costumes, like the arms, legs and torso if inside a business suit, for example. If it doesn't have to calculate textures, or a lot of them, you'll definitely see a speed increase.

The cube enclosure does work, but it's best used for scenes with props that are out in the open (the theory of scene enclosure is that Lux uses 'photons' of light to bounce around your scene, then traces their intersection with obstacles, ala characters and props. When these are out in the open, the photons bounce out into space, rather than being enclosed, which lengthens render times.) If your charcter is already in a room, a cube isn't really needed. Or if your scene has an incomplete set of walls, like a corner piece, just add scaled flat plane primitives and set them to matte in Reality.

It's little tricks that add up in the end in the name of efficiency!

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