Cut down the size of what you're doing. Try for a simple face portrait, with a single spot. Don't pose the face at all, leave it at the default. You can work on expression later. Shadows are more emphisized this way. Remember that a low res texture will need a bump to give the face some texture. Also add a light sheen to the skin, otherwise the texture can look like it's been powdered. Here's a low-res free face with a problem on the lip mapping (Superman) for Mike 2. I used a single spotlight (white) pointed at the face to the upper left. Large highlight size, with a light grey color on the sheen. I mapped the bump back to the texture, but used a low level. No face posing, just a twist and bend in the neck.