The hair dynamic calculation seems more slow since SR4, I dont yet verified if the problem persists in SR4.1 I use hair room following this method: 1. Create more hair groups keeping separate the ones with hair that could be involved in collision. Using more group its also useful for other reasons: you can do a better distribution of the hair density; its easier styling the hair etc. 2. Do dynamic calculation without collision checked (its fast); 3. Find the hair that intersect body parts, select them and remove intersections with hair styling tools (shorten the strand, bend it etc.); in order to use styling tools, you have to clear the dynamic calculation for the involved groups; 4. Redo dynamic calculation with collision checked for the groups that can collide (not for other group). I hope I was clear: Im Italian and my English isnt very well