I also find that premium diesels such as BP Ultimate diesel or Shell V-Power diesel improves the smoothness of the engine, especially if you usually do short runs. I use them whenever I can find them, my first choice being the BP. We also have a diesel X3 without DPF and you can really notice the reduction in black smoke on hard acceleration from low revs. Other benefits of the premium diesel is extra power and in my case, better fuel consumption.

Whenever I cannot get hold of premium diesel I add Millers Diesel Power Sport 4 to the tank. It smells just like the BP Ultimate so I guess it could be the same thing.