My 2006 X3 at 118,000 miles is running great. So, today I replaced the original OEM Bosch plugs. I used NGK Laser Platinum, also OEM plugs. They were $38 for 6 of 'em plus tax on Amazon. Whole thing took about 45 minutes. I left the strut brace in place. I did remove the cabin air filter housing to get to the back 2 plugs/coils. It is only 4 T30 screws to loosen and only adds 10 minutes to the job (I cleaned out all the leaves and pine needles and spray detailed it before reinstalling). My coils were easy to remove by hand. The plugs came out easily. I have been averaging 25.5 mpg on the highway with the old plugs at 70 mph (just got back from a 900 mile trip to drop daughter off at college with a full veheicle.) The old plugs looked pretty good at 118K miles.

NGK BKR6EQUP 3199 plugs.