In my article Custom Properties Demystified I reference a chart I put together that defines the override order of custom properties based on where they are defined. The document is available in the downloads section. This document is a list of my findings based on testing I performed.
While delivering a vCAC 5.1 training class today I shared the document with my class and one of the attendees was kind enough to look over the chart and determine a definitive override order based on the data. This is great as I never took the time to review the data to determine a definitive override order. So here you go.