The maximum pressure is going to be either: 1. the relief valve spring setting, or 2. the highest the pump can deliver if the bearings are really loose, SAE 5 oil, etc.
An exception is where the bypass port is simply too small to dump enough volume (almost all stock pumps), and pressure rises above the relief setting. This is why you see these comments: "My cold pressure is 70, but when it warms up it's 40". This is not poor quality control or a defective pump: it's a design error.
