While that 5th day is up in the air, it's difficult to suggest how to best divide your route. You should certainly look at the map and find places that are interesting to you and then see how you can make that fit into your final plans. It looks as though LA is the first night for sure. If you have 3 days for the remainder then around Tucson and Fort Stockton would makem reasonable overnight stops. You could push on a little further but for night 2, Las Cruces would be a real stretch, and beyond what we would recommend to travel in a day.

With an extra day you could play with your options and see what suits your tastes in other areas.