Mobile 1 is offered in a 5W-50 grade; it's just not readily available here in the states. You can buy it mail order though. The Motorcraft 5W-50 and Castrol Syntec 5W-50 are the only oils that I am aware of that are certified to comply with the Ford WSS-M2C931-B spec for 5W-50. There are several 5W-50 synthetic oils that exceed the spec but certain aspects, such as higher levels of Phosphorous (in ZDDP), probably keep them from fully complying, plus the cost of certification may be prohibitive.
http://store.avlube.com/mobil15w50.html