I took delivery of my twin turbo last weekend and had a 535d for three years so am very famiilair with the engine. I have also driven the 3.0d version of both cars.

The main difference with the sd is how it accelerates in gear and also how it keeps accelerating right up the rev range like a petrol engined car. The 3.0d starts to feel flat further up the rev range and running out of puff like a normal diesel. The 3.0sd also feels smoother and sounds much sportier.

In the UK the sd is around £2000 more than the d. To me that's a bargain by BMW standards as it also comes with bigger brakes.

It's an absolute no brainer unless you are on a tight budget. My 535d also kept it's value extrmely well and is in decent demand which bodes well dor sd residuals I reckon you will get all of the £2000 back if you sell with say 5 years. My 535d kept 63% of it's value after 3 years which is absolutely outstnading for a large mass market car. Small BMW's don't do that.