Amsoil is an outstanding oil I prefer 5w30, and in the Amsoil line 5w20 is only avail in the 7500XL series which seems to be a lesser oil than the regular synthetic they have based on thier change intervals of 7500 vs 25,000 miles. Given that , I prefer the Amsoil 5w30 for the C though I would never go 25K. I have gone 15K in the leased X5 which is what BMW requires in their free maintenance plan (so generous, two free oil changes over 36K). An excellent alternative is Mobil 1. Check the thread on oil filter magnets.