I have a 2014 F800GT with the standard BMW hard panniers, but no rear case. And I intend to keep it that way. However, I am looking for a rack to add to the top of the current, stock, luggage rack at the rear. I would like to add some width and tie down points for carrying 50 liter waterproof compression bags.
I have two; one for my camping gear, the other for my clothing/jacket/boots etc. I usually make a couple of 2-3K mile trips every summer, and camp for most of the distance. The panniers carry my heavier or more valuable stuff; tools, spare oil/water, cooking gear, food, electronics, etc.
I had a F800ST with the BMW hard panniers and a Givi topbox for a number of years. Great box, waterproof, with lots of room. But a sail when the crosswind kicked up. Since I live in Minnesota, on the edge of the Great Plains, this is a common problem. Hence, the shift to the 50 liter compression bags.