[cobrin]

Ford WSS-M2C913-D
Introduced in 2012, oils meeting this specification are recommended for all Ford diesel engines except Ford Ka TDCi models manufactured before 2009 and Ford Galaxy 1.9 TDi models manufactured between 2000 and 2006. A product meeting this specification is especially recommended for diesel engines where M2C913-B or M2C913-C oils were initially required. An oil meeting this specification must be used in Ford Transit vehicles manufactured from 2012 onward with Duratorq 2.2 engine. Oils meeting this specification can be used with extended oil change intervals and are also suitable to be used in engines running on biodiesel or high sulfur diesel.

Ford WSS-M2C950-A
Special engine oil for Ford Focus Diesel 2.0 manufatured from September 2014 and Ford Mondeo Diesel 2.0 manufactured from 2015. Viscosity should be SAE 0W-30.

Essentially 913D is a slightly thicker grade (5W30) giving a HTHS viscosity between 2.9 and 3.5 mPa.s, where as the 950A will be 0W30 and have a small improvement in fuel economy over 913-D and have a lower HTHS level which i can't currently find. You should get a small improvement on fuel consumption but you might burn a bit of oil in the service interval so monitor, protection wise wouldn't be much of a diffference but if there is any it'll be less protection at higher temps but not enough to damage the engine (IMO). I stick to to 913-D as it's easier to source and no real tangible benefits to be had from 950-A.