These guys are very good indeed. Give them all the information and follow their advice. I'm currently using Shell Helix Ultra 5w/40 in my 528i under their guidance and it works very well indeed. BMW suggests 5w/30 but I have not noticed any downturn in performance or economy with a slightly heavier 5w/40. Prices are good, too. Plus, you'll also get a discount for being a Torque Cars member.