First of all, sorry for your e90 troubles. Thank you for sharing, your experience will help us deal with the problem should it happen to any of us (knock wood).
Was wondering if your car is step or non-step. On an unrelated issue/problem and purely fyi, a 325xi non-step owner complained about his car's engine cutting out above 4k RPM at certain altitudes. He went on to say there have been up to 5 cases of 325xi's manuals with the same problem.
http://www.bimmerfest.com/forums/sho...d.php?t=143328
Is there something going on with non-step 325xi's? You might want to keep a close eye on the problem...