Going with a stiffer (I am sure that is not a word) bar in the rear would induce more oversteer.
I am a fellow stocker though in DS.
Did you also consider the H&R front bar? How do you like the car with the larger front bar? This is likely the next thing that I will do. This and Konis. You are running Konis if I am not mistaken. Did you get the singles or the doubles? How do you like the Konis?