One thing I have noticed about these threads is that most people who prefer BP Ultimate Diesel seem to be driving the 6 cylinder models, while quite few 320D owners appear to be the opposite. Could be random ....
I had to use Shell Vpower for the last 2 months as my BP garage was renovated. In my 335D I didn't like the Shell Diesel - seemed to be less smooth and steady with power delivery - more peeky and made the gearbox hunt a little more.
Now back on BP for a couple of tanks and silky smooth, with rock steady smooth acceleration from low revs.