You should not be running winter diesel in your X5, its designed to run on Ultra diesel. Your ultra diesel in the US is 15ppm and that is the highest rating you should go.
Here in Australia our ultra is 5ppm thats partly why we get the 40d & M50d engines. Uk & European ultra is 1-2ppm.
The 40d & M50d use different injections, rail pressures & higher turbo pressures, winter diesel depending in which country you are in could be 50ppm & 500ppm, we refer to this as semitrailer truck diesel fuel.
I run this in my 1974 FJ40 2H Toyota Diesel as it has an old fashion injector pump.
I read alot about the amount of smog gear you have on your X5 diesels & owners complaining about the black on the rear of the X5, as we have only 5ppm of sulpher and harding any smog gear we have little black dust etc .
X5 F15 M50d White, 20"rims, Yellow Calipers, Ceramic Pads. Better off saying what it does not have and that's a B&O Audio System, other than that every option box is ticked.