Very much depends on the country where you live, km / year and what you do with your car. Here is what I'd suggest you consider, and put together a table to compare the figures:

• Annual insurance
• Annual road tax
• Monthly payment (if you plan to take a loan or lease) differential
• Fuel differential ( L / km) with your annual driving
• Road tax & pollution surcharge (depending on countries) of your two alternative X5 choices.
• Annual servicing
• Depreciation - if you compare the same year and the 3.5D vs. X5M
• Tires - part of your annual driving & style calculation