Go with the Castrol (or whatever has the lowest calcium). If you don't, it will bother you and make you continually second guess your choice throughout the OCI. There's no need to subject yourself to that kind of stress, so just go with the Castrol.
Personally, I will never use Castrol again though. Last time I tried Castrol at an OCI, my grandmother ended up passing away within a few months. I've only got one grandmother left, and I ain't taking no chances, so give me anything BUT Castrol!