Let's look at it this way. Forget the fuel savings arguement. The 35d will be .5 secs slower to 60 than the 4.8 and cost about $7,500CAD less (assuming a $4,000CAD option cost). It will be $,4,000 more than the 3.0si and 1.0 sec quicker 0 - 60.

BMW tends to price cars by performance, so I think the 35d is a pretty good value, compared to the 4.8. It is reported to have better low end torque than the 4.8 making it great for city driving. Also, given fuel mileage reports from owners of 4.8's that "drive" them, fuel mileage can be as bad as 12 - 13 mpg. Diesels just seem to perform better when pushed than gas engines and with 450 lb. ft of torque, I don't think you'll be pushing the 35d as much as the 4.8.

I'm looking for efficient utility. If I just wanted to go fast, I'd get a 5 series.