Quote - These are the render settings. Does anybody have an idea what specific factors could be causing it? It always takes so long to render with this hair, I'd rather not have to do very many test.

 

Increase ray depth to 8 minimum, and rduce filter sharpness to 65=70%.  This gives the room a slightly warmer more realsitic look.  Also make sure you dont have something in your scene settings as a background.  An image map in there or some kind of procedural could cause problems like those spots.

If you are using realistic sky or sky, just turn it off since it will not really show in the render with the camera angle you are using.