BMW six cylinder diesels are pretty robust, in my experience. I get 33mpg (imperial) from my E53, but would advocate oil and filter changes mid-way between the service indicators.
My old 525 E39 turbo diesel ran to 204,000 before being sold, it needed glow plugs at 160,000 miles.
The choice of diesel here in the UK is purely economic: more than 12,000 miles each year makes the extra outlay worth it. While my E53 can be entertaining, for fun I take the M3 or Z4.

OP in your ncknof the woods the stop and go traffic will b killer mpg wise if u go with a diesel. I recently traded my 2012 x5d base model for a 2015 x5d. If u do a lot of long road trips further down south or out west, the diesel would be the better option. On recent trips from NYC to FL I saw 33mpg once I got thru DC area. That was at 75mph with cruise control engaged. Letting the x5 think for itself, I feel is key for optimal mpg. On the way back to NYC I ran it at 85mpg w/o cruise control and saw 30mpg which is still respectable for a 5000lb vehicle. I put just under 40k on the 2012 and owned it out right for just over 2yrs. I ordered the 2015 with M pkg, driver assist pkg, convienence pkg and upgraded to be 20" wheels and multi contoured seats. I'm happy with it so far. I have 5k on it. What I liked about the '12 was its styling and the brakes. I'm not into tech stuff so the iDrive system doesn't do anything for me. What I didn't like on the '12 was the drive by wire system. I'd have to keep it in sport mode when starting in traffic. Felt like there was a slight delay when applying the throttle. Sport mode minimized the jump in torque. The '15 brakes r smaller and the throttle delay is still there but it's not as harsh. Once in sport mode you don't feel it like in the '12. All of the 12s short comings are eliminated in the '15 too. Larger NAV screen is nice too. If your into music do t go with the stock system. I could t justify paying 4,500 for the Bang&Olfsan system but wish I did lol. As far as maintenance I only had to go I for urea top off. Sercive intervals were the same as the gas motors. All in all the 15 is a nice looking and very comfortable vehicle. I prefer the e70 looks over the 15 but it's everything the e70 isn't.

Just picture me fueling up the Peugoet 504 D in the mid 70's. It was during the fuel crisis. When I did use a gas station
I made a lot of people mad driving up to the diesel pump until they found out the pump I was using was diesel.
I also knew where all the truck stops were. Now days Diesel Is everywhere. :thumbup: