[SkipSauls]

I don't have the source handy, but a while back I saw a post where someone explained that the 40d and 35d are actually quite different. The 35d is based on the "old" (10+ years) M57 engine and the 40d is based on the newer N57. All of the urea-injection technology works on the M57 and has not been released/certified for the M57, so the US gets that engine. I believe that some/all of the 3.0L diesel engines for other markets are based on the N57, but it simply can't be dropped in and shipped for the USA.

To make things "worse" for those of us in the USA, the 8-speed transmission was designed for use with the newer gas and diesel engines and cannot be easily retrofitted to the older M57. With the 3 series and X5 being updated over the next couple of model years, it may be that BMW waits to introduce the N57 in the USA with those models.

After owning a 2011 35d for the past 10 months, I'd tell anyone considering one to not worry overly much and just get it. They're not speed demons, but they'll get out of their own way nicely, can outrun most traffic, and will easily reach "take my license away" speeds with very little effort. The 6 speed is smooth, the engine makes a nice sound that is reminiscent of a V8, and economy is decent for a 2.5+ ton vehicle. Would I prefer a 40d with the 8-speed? Sure, but I'd also like an X5 with a 2.0L 4-cylinder tri-turbo hybrid diesel-electric, 40+ mpg, a weight reduction of 1000 lbs, complete LCD multi-touch dash, and so on, but I am enjoying my X5 now.