I have filled up my fianceŽs 125i with Mobil 1 0W40, it will be my testmule
It may be not very objective, but I could have sworn that the engine now runs smoother than with the OEM Oil.
Although the oil has been changed on a regular basis, when I opend the Refill-Cap ontop off the engine, it was completely coverd with kinda big lumps of oil.
Cold starts now seem to be "easier" for the engine too. IŽll keep you updated