When the engine was designed 0w-30 c1 probably didn't exist.
I used to run a Ford Focus st mk2, which shares the same block as the rs. The st uses 5w-30 as standard but most tuned ones are run with rs-approved 0w-40. My understanding is that the cold temperature viscosity is lower but high (working) temperature viscosity is a bit higher. This provides less friction at startup but better protection when being worked hard.
Providing it is low saps, 0w-30 should be better for a car that does short journeys, however I am happy to be corrected by an expert.
https://www.opieoils.co.uk/p-205731-total-quartz-ineo-first-0w-30-advanced-synthetic-engine-oil.aspx
The above looks interesting and even had a jlr approval.
