What's your problem... Ace.............. we have a nice friendly board here, and once in a while some Jerk comes in and thinks he knows more than others......and that would be d Geek.... I don't know why you're on this board, since your an avid TDI geek, but for the vast majority on this board that have never driven a diesel, nor owned one, I think its a great way to learn about what to expect when they spend upwards of $60K on a new vehicle.
For those that aren't as smart as dGeek. The reason the federal mandate on ULSD with 15ppm of sulfur is to allow the use of a diesel particulate filter to eliminate the PM content of the exhaust. If you use diesel fuel with higher concentrations, you'll poison the diesel oxidation catalyst, and ruin the exhaust system. A hefty, non warrantable repair. You can decide to use off-hwy fuel if you have access to a fuel tank on a farm or construction site. This fuel is dyed red to identify it as being 3,000 ppm, and exempt from federal hwy taxes. It will ruin your exhaust system, and if you get caught using it as an automotive fuel, there are big fines to pay. And if you only use it once, the red dye will linger in the fuel tank and continue to turn the fuel red for some time. You can use ULSD in vehicles older than 2006 without any issues.
Another issue to concern yourself with, is the use of Diesel Exhaust Fluid (DEF). This is a solution of 32.5% Urea with distilled water that while in solution, will freeze and thaw at the same rates, making it usefull in all climates in North America. The EPA granted the use of DEF in the SCR portion in the exhaust to control NOx to near zero levels. If you choose to home brew your own DEF and use in your $60K vehicle to save a penny or too, beware that if you're out of concentration, or if you use tap water, you'll build up scale in the DEF doser, and cause expensive repairs as well. I believe the DEF tanks on the X5 approach 6 gallons total. The ratio of DEF to diesel fuel is 2 - 3 % on heavy trucks, and likely less than that on an X5.
So, the EPA begain the journey to reduce NOx and PM back in the 1970's, and 2010 is the big hurdle for on-hwy trucks. Fortunately for us that are awaiting X5 35d, the path to ULSD did indeed begin in April of 2006, when the east coast and southern refineries stoped refining 500 ppm fuel, and began to produce 15 ppm ULSD #1 diesel (also known as Kerosene). The drawback of 15 ppm is the lubricity that sulfur provided to fuel, and all suppliers add a lubricity additive, not at the refinery, but at the local bulk fuel rack in the area that services the fuel stations in each major depot.
The long and short of it, just so d Geek understands it all, is that you shouldn't be afraid to purchase ULSD at any truckstop on a US interstate, or at your local Shell or Mobil station in your neighborhood. If you choose to go the biodiesel route, a B2 to B5 blend is probably nothing to worry about, as long as you're buying from a quality supplier. You'll pay a premium for biodiesel, and I'm not convinced that spending and extra 20 - 30 cents will get your much in the way of lower emissions or less dependence on foreign oil.
Hope this helps. Not that it matters, but I've been in the diesel business for over 30 years, and live this stuff every day.