Shading rate shouldn't matter too much on complex polygon transmapped hair models. They have many angles and vertices running around in them, most of them bending far above .2 relative to each other, so if you bump the shading rate up a bit, it shouldn't make a huge difference. (Individual mileage may vary. Hair with very subtle bends in it, like long, straight, hair, might need lower shading-rate settings to pick those differences up.)

Light Emission is the killer. For me, I don't see the need in making most hair an emitter. Why? Because, it's all fairly unrealistic anyway and with closely bunched up polygons, many times intersecting each other, it's an effort in futility that yields little in the way of meaningful results. A good material set can take care of just about everything you'd want, anyway. And, a very good transmap, too.