I agree if the car is being used on a daily basis the M50d would probably be a more practical option that the X5M, especially when doing higher mileages as the fuel consumption is a lot better and that torque is great for overtaking
and it's probably a lot better on depreciation as there is a higher demand for diesels at the moment.However, I think we are now all concerned about the future of diesels as there are so many on the road after the government encouraged them with lower co2 emissions originally, but they have now started a u turn. This knocks the market and the consumers view and confidence which the uncertainty brings. I even remember that some people on here with diesel X5's have commented they would think about going petrol next time because they are doing less mileage.
So you pay your money and take your choice. Whichever one you pick they are nice cars to drive, and for shreksta as he said he is only doing low mileage about 80 miles a week it's a tough decision to make. As Condor said it's best go and test drive them whether a petrol or a diesel one and you will know which suits you best.
Re the stonechipping problem,
the E70 also had this problem and BMW repaired the areas (repainted them) under warranty, due to the large 20" wheels, and then fitted the bad road package basically clear plastic film to the front of the rear doors and rear arch and rear of the sill to protect them from damage.
Graeme
So it may npbe worth looking into that to help or fitting mud flaps which don't look grapeat but are functional.
Never anthropomorphise computers. They hate that.