I'll take a stab at answering this one. I hesitated because I planted evergreens on my hill (pine, fir, spruce, and hemlock). My slope sounds like it is very similar to yours. I planted 13 evergreens 3 years ago and so far so good. They are growing straight, and seem firmly imbedded into the hillside. We planted evergreens for two reasons: it's on the north side of the house and we wanted to protect the house from the winter winds, and we're hoping that as the trees get larger the maintenance of the hill will decrease. Currently my husband has to weed whack the hill because it's too steep to mow. Since you didn't get much response you might want to post in the trees forum. Good luck.