As said my friend who told me not to use Castrol didn't give me an explaination, i just took his word as he is quite worldy. He was the one that actually recommended Fuchs as he uses it on his M3 and 325touring but thought i'd get the SN masses opinion.
Alfa romeo recommend 10/40 semi synth Selenia motor oil but i think its more to do with them being owned by Fiat/Alfa at one point.