My concern is regarding PBNs. Its always better to get a domain more relevant to whatever your niche is your linking out too. How does google actually determine relevancy when linking two sites together? Im not talking about anything on the site, like the post titles or content. I'm talking about determining how each site is relevant to each other. It seems to be clearly implied the more relevant the sites are the more ranking boosts you will get. Why? Does google look at each sites anchors and go, okay they're all on a similar topic; +3 ranking points. What exactly in the algorithim determines relevancy and what exactly gives it any more of a "boost" then two sites on completely different topics linking to each other? Unless theirs a specific answer to this, I'm starting to think its all hearsay. And G is more robotic than we may think, as it comes down to pure metrics more than anything else.