The difference between the C2 and C3 is the HTHS the C2 @ 2.9 mPas is designed to prioritise economy over lubrication performance. C3 having a slightly higher HTHS @3.5mPas will protect the engine better during use.
With any multigrade oil the larger the difference between the winter and high temp grades means there is a larger amount of the Viscosity index improver to make the oil perform better particularly at super low temperatures the like of which we never see here, I am talking about -35°C and -40°C which is where 0w and 5w are tested on the J300 SAE scale.
The first part of the oil to break down is the VII so the oil which has a larger range will break down faster than the oil with a smaller range.
At -35°C 0w has a pumping viscosity of 6200 mPas and at -30°C 5w has a pumping viscosity of 6600 mPas, these temps are very low, at -5°C or even -10°C the difference is very small, and unlikely to mean much to a normal passenger car driver.
in my view given I never see temps below -15°C I prefer to use an oil that has less of a range between the winter and high temp rating as I don't believe there is any benefit to my engine in using an oil rated for -40°C over -35°C.
I am far more concerned about using an oil which provides better protection during use which is the difference between the C2 and C3 Acea ratings and the difference in price between a 0w30 C3 and 5w30 C3 is usually quite significant.
and enables me to use smaller Oil change intervals which I prefer.
Like most oil threads people have their own opinions and ideas and I'm not stating mine is right, I just don't see the need for me to use an oil that is designed for use at temps far below what I normally encounter.
If I lived in Canada or Siberia I might choose to use 0w30 but as I live here 5w30 C3 is more than enough for me.