LiPo current ratings and true continuous limits

I see that many LiPo have high C ratings and when multiplied by the amp hours they claim a high continuous current capability. I have two questions. How realistic are those ratings and are some brands better than others? And secondly, if they come with an XT90 connector surely as they are rated to 100A at 80C continuous and that becomes the current limit no matter what the label on the LiPo claims?