We have a similar sort of hillside that doesn't sound nearly as big by any stretch of the imagination but our hillside is covered with three groundcovers -- vinca (myrtle), lily of the valley and pachysandra. All three of these do well for us. We are in Central New York in zone 5. I also like the fact that all of them have a blossom. The lily of the valley is best with leaf cover becasue it comes up every spring whereas the other two are there constantly. The lily of the valley pushes its way up through the leaf cover and is no work! -Amber