Hi Sam
My brother-inlaw's 5 series touring (same engine) uses Castrol Edge 5-30 M. Have you checked your hand book there is normally a list of oil spec's listed.
I believe you need an oil that meets BMW Longlife 04 spec's for the M57TU2 which most of the major manufacturers meet. You could also look at www.newtis.info it is a BMW technical information site so you should be able to get service information there as well
Hope this helps not hinders
Dave