Different car, but I'm doing 7500 mile ocis on my turbo charged volvo S60 using M10W40. Two used oil analysis suggest that the oil has plenty of life at 7500. The only reason that I'm sticking to 7500 is that the car is covered under an extended warranty and 7500 is the Volvo recommended oci(Volvo specs semi-syn for my car). If your car is under warranty, I'd go with whatever BMW recommends. If not, I'd go 10K and do a used oil analysis. I'd be willing to bet that for the 0W40, 10K will be a breeze. If BMW has an olm, I'd go by that and maybe change at a little higher % than what they recommend.