I used Mobil 1 0W40 (now switching to GC 0w30.) Smoother idle when the A/C is running flat-out in middle of the summer as it's a bit thicker at high temp, plus better cold start lubrication as it's thinner when cold - truly a no brainer. Only downside might be very slightly higher friction and less gas mileage, although I didn't notice a hit when I changed from factory 5W30 (but it was summer in AZ), consider also that BMWs are developed in Germany with short, mild summers, and not FL or AZ. I'll change mine every 7,500 mls (as I did with my E46 with M1 0W40.)
I'm a fan of the magnetic drain plugs, it's a good way to see what's going in in the engine, and get more junk out - Turner carries them.
Last edited by AlanAZ; 04-28-2012 at 12:33 PM.
Reason: more info