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.
Yes, the 5w20 DC recommends is for the EPA, not necessarily the ideal weight for summer use. The MDS with it's cylinder shut off gives concern about too thick oil but multi vis solves this since it is still 5w, it's not like running 20w50. I may run 5w40 spring.summer and use 5w30 or 0w30 for the Ohio fall/winter. Will likely change twice a year. I will probably have the dealer change at the scheduled interval with my oil and filter for documentation purposes while under warranty and do my own otherwise. If you have not checked the oil filter study do so. Amsoil also makes a great filter as does Mobil 1 (champion labs) and WIX/Napa gold. http://minimopar.knizefamily.net/oilfilterstudy.html
No. My research on the 300C filter 5281090 at Amsoil indicates an SDF 42 is the correct one or Mobil 1 M1-204. The same filter for the 300M,Jeep,Hemi Ram. You will want to confirm this with amsoil before you buy. I can't wait to do the first change.