I would like some opinions on the following. Regarding my 2011 Fusion, Ford specifys a 10,000 mile OCI using any conventional 5w20 that meets the Ford spec WSS-M2C930-A. (The car has the new intelligent oil life monitor that reduces the OCI based on driving conditions; for my mostly-highway driving conditions it dictates a 10,000 mile OCI.) How many miles would you all be comfortable running a major brand of synthetic oil out to? 15,000? 20,000?