The new generation diesels everyone is making are all great engines. Depending on pricing, etc, a diesel would be high on my choice list for something like the X5. I've owned a couple of Dodge diesels, and those engines are incredible, the '05 in stock form would pull that 7200 lb truck past 60 mph in about 7.5 secs and still get 18-19 mpg on the highway, which is more than my X5 gets! 650 lb-ft of torque is wonderful thing!!
And the new diesels are quiet, don't smell and are easily upgradable to get even more power.

All diesels sold in the US from 2007 model year on are burning the low-sulfur diesel, so yes, the BMW diesels will be low-sulfur