Napa synthetic is NOT relabeled Synpower. They are both made by Ashland but are different products. Someone on this board did a VOA of both products and Synpower is far more robust.
I am the one that did the VOA on Synpower and Napa syn 10w-30. I would not say that Synpower is 'far more robust'. I would be inclined to say they are different formulations. I have used both on 5K OCI's and noticed zero differences. I also did UOA's on them and both preformed fine.