That's not just an opinion, it is a fact.
IMHO, the OP should NOT worry about a group III base breaking down excessively. The properties of the group III are VERY different than the commonly refined group I and II bases, despite all 3 groups coming from a petroleum base. Not breaking down (or oxidizing) excessively is one of those special properties of group III bases.
Read here and you will see that this is true.
Performance of Base Oils and Future Trends - The Evolution of Base Oil Technology - Part 3
Castrol Syntec is a Group III base. I have yet to find what the base is for VR1.
