I bought 1.5x5's and 1.3x6's. I replaced the conventional 1.5x5's that I had in my D815 with VRP's 1.5x5's. I haven't had a chance to test the 1.3x6's yet.
The pistons aren't going to solve your loose rear end on your B3, but they'll get you through the rough stuff a lot better. My buddy's got the same car as you and loves the pistons.